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By P. Talonen

Since the last Iron Control in Hydrometallurgy Symposium in Montreal in 1996, the Kokkola zinc plant has increased its capacity from 175,000 t/y to 280,000 t/y by installing an atmospheric concentrate leaching process, which has also affected iron control in the leaching circuit. Major changes have been made at the jarosite residue pond; a subterranean plastic wall reinforced with bentonite and cement has been built around the pond. A new water collecting system that is used for groundwater level control in the pond area was installed. With these two investments in the pond area, it is now possible to prevent any seepage flow from the pond into the surrounding environment. Water pumped from the residue pond is treated in the water treatment plant. This paper describes the behavior of iron in Kokkola's current leaching processes. The treatment of the jarosite, the improvements to the residue pond and the water treatment process are also described.

Jan 1, 2006

By Frank Ebbutt

Introduction The property of the Britannia Mining and Smelting Company, Limited, is situated on the east side of Howe sound, about six miles from its head. It is roughly thirty miles by water from Vancouver, one of the important ports of the Pacific and the industrial and financial centre of British Columbia. Howe sound is navigable for ocean-going vessels and Britannia Beach is a daily port of call for the commodious boats of the Union Steam-ship Company, sailing from Vancouver. Few mines are so ideally situated or have so many or varied natural advantages. Copper was first found on Britannia mountain in 1888, by Forbes, but it was not until 1898 that five claims were staked here by Oliver Furry, a trapper. It is from these claims that the major production during the past thirty years has come. In 1900 the Britannia Copper Syndicate was formed and development of the property was commenced. In 1903 the late Grant B. Schley obtained control, and through his efforts the Britannia Mining and Smelting Company was organized in 1908 as a subsidiary of the Howe Sound Company. Since that time, a persistent and progressive policy has been followed, which has resulted in a prolonged and profitable operation. The country in the immediate vicinity of the mine is marked by strong relief, with mountains rising abruptly from tide-water to elevations of 5,000 feet and more. Two broad transverse valleys deeply dissect the area. These are the valleys of Britannia creek and Furry creek. The region has under-gone prolonged and relatively recent glaciation. Over much of the surface there is deep overburden and dense vegetation. The geology of the mine and vicinity has been described in reports by S. J. Schofield (1), H. T. James (2), J. G. Barry, and others (3). The present writer is in accord with much of this literature on Britannia, but during recent years, extended observations made underground have shown that the 'quartz porphyry', or 'mine porphyry', of several of the earlier writers is not the host rock to the commercial mineralization; and he contends that the mineralization occurs in highly altered phases of a complex series of ruffs, flows, and pyroclastics and their autoclastic metamorphosed products.

Jan 1, 1935

By Edward Sampson

Bases of National Power At a time when the economy of the world is in a particularly troubled state it is appropriate to examine some problems of the distribution of natural resources. I should like particularly to call attention to the remarkable increasing demand for natural resources, to give an analysis of the demand for certain mineral resources, and to direct attention to some problems in satisfying this demand. All industrial power is based on natural resources and the most basic of these are soils, energy resources, and mineral resources. There is a strong interrelation of these resources, more than is obvious, and I shall take up certain aspects from the point of view of a geologist. Few nations are well endowed with all three of the kinds of natural resources I have mentioned and much has been done by some small countries whose peoples are industrious and enterprising and where conditions for free world trade have been favourable. However, major industrial power is dependent on a substantial endowment of all three classes.

Jan 1, 1949

By Xuanxue Mo, Kaihui Yang

"Abstract- The Laochang mine, located in the Sanjiang area of southwestern Yunnan Province of China, is a volcanogenic massive Pb-Zn-Cu sulfide deposit. It is hosted by a pyroclastic sequence of Barly Carboniferous age, namely the lower member of the Yiliu Group, which was intruded by syenite and rhyolite porphyry . The volcanic suite is basaltic or basaltic-andesitic in composition, has alkaline affinities, and is associated with the initial rifting along the margin of the Baoshan-Shanstate continental rnicroplate (Yang, 1989). The ores are typically Pb>Zn>Cu in composition, averaging 3.820Jo Pb, 3.51% Zn, from 0.01% to 1.85% Cu (0.107% av.), a high average content of Ag (113 g/t) and recoverable amounts of Au, Tl, Gd, Ga, Ge, In. A massive sulflde zone, in which lenticular and stratiform orebodies are localized in a sulflde-carbonate-silica shale unit or sulfldic tufflte horizon that usually overlies coarse-grained pyroclastic rocks, is underlain by a stringer sulflde zone developed in a subvolcanic intrusion or volcanic sequence. The sulfide mineral assemblages, from the top to the bottom of the deposit, are: realgar + orpiment - galena + sphalerite + pyrite- chalcopyrite + pyrite + pyrrhotite + arsenopyrite. Oxide and sulfate minerais occur rarely in the massive ores. The massive ores are generally fine-grained and banded, but coarse-grained ore, colloform and framboidal texture, and growth-zoned pyrite and sphalerite are common. Sedimentary features such as graded bedding, brecciated and deformed ore clasts, and chaotically emplaced blocks, are well preserved, indicating that the massive orebodies have undergone slumping and dis­ placement. Alteration is weak in the hanging-wall rocks, but strong in the stringer zone. Two dis­ tinctive alteration zones have been identified: the upper zone, characterized by an assemblage of quartz, carbonates, chlorite, albite, zeolite and sericite, and the lower zone containing diopside, trema­ lite, actinolite, gamet, clinozoisite, and epidote.The general features of the Laochang deposit are in accord with the descriptive mode! of VMS deposits (Lydon, 1984). However, it falls into neither the Zn-Cu group nor the Zn-Pb-Cu group chemically (Franklin et al., 1981). The depositional setting of the Laochang deposit is quite different from Cyprus or Besshi-type massive sulfide deposits. Laochang is hosted by alkaline lavas that were erupted in a submarine continental rift. Although some features of the Laochang deposit are similar to those of Kuroko-type deposits, there are remarkable differences in the alteration mineral assemblage, the proportion of ore-forming elements (lead enriched) and the amounts of oxides and sulfates. These suggest corresponding differences in ore fluid composition and the associated ore-forming environment. Thus, the authors suggest that the Laochang deposit may be a distinct type of VMS deposit."

Jan 1, 1993

By Deepak Bhadouriya, Saurabh Singh, Aditya Raj Suman

"An experimental study of chemically enhanced filtration and dewatering of fine coal slurry with and without additives was carried out. The experiment involved determination of effect of slurry concentration, additives (cationic, anionic and nonionic), filter area, filtration velocity, particle size and cake resistance on dewatering and filtration using vacuum filtration cell. Finally, the rate of filtration and dewatering and optimum amount of additives used were determined under suitable filtration condition. Overall, it was found that the filtration and dewatering characteristics were enhanced by increased slurry concentration, larger filter area and larger particle size. In addition of additives, the kerosene was found to be best for enhancing the filtration which yielded cake moisture reductions of approximately 17% by weight. At optimum dosages, the final cake moisture contents were reduced by 3.6% and 5.8% by weight using the appropriate surfactant and flocculent, respectively.INTRODUCTIONFor India, it is estimated that coal constitute a principal source of energy for the next several decades. It is majorly used at thermal power plants to generate electricity and also to a great extent in steel and cement industry. It has been observed that its consumption is increasing so as to meet the energy requirements of the country. It has been found that in a coal preparation plant; approximately 20-25 percent coal is of the mined coal of the range below minus 0.5 mm (28 meshes). Generally, this fine fraction is discarded due to its high cost of processing and further utilisatisation is very minimal. But with ongoing research and development for advanced clean coal technology, various new techniques have been evolved to maximize the utilization of available coal. In recent time technologies such as column flotation, cleaning of fine size coal to lower the ash content and low pyretic sulfur is feasible at high recovery value. But in various researches it is found that one of the biggest hurdles in utilization of fine coal cleaning technology by the coal industry is the economic dewatering of the fine clean coal product. Thus, until an economical and practical solution to dewatering of fine clean coal is achieved, the efforts devoted to developing fine clean coal technology will be wasted. In this paper an effort toward enhancing and developing the optimum technique of dewatering and filtration of fine coal slurry has been made."

Jan 1, 2016

By E. W. Thorton

"This paper is intended to show that grinding media can effect flotation results, and in some instances the results are vastly different. I do not suggest that autogenous grinding is beneficial in the separation of all complex base metal ores, in fact I know of a case where autogenous grinding would be disastrous to any selective flotation. I do however contend that prospective flow sheets and reagent balances of any complex base metal ores should be tried with both types of grinding. I feel fortunate that the paper to be presented later in this meeting by Rene Klymouski will, I think, compliment and perhaps explain some of the results of my research.This paper will be in four parts. The first part deals with a literature survey on the subject. Surprisingly enough, very little information has been printed on the subject. The second part deals with results obtained in bench scale tests on an ore from Chester Mines Limited. It was in these tests that we realized that steel grinding was giving us serious problems. So bench scale tests are shown giving results with a stainless steel grind, a mild steel grind and a grind in a ceramic mill with ceramic billets.The third part of the paper deals with results obtained in the Mines Branch Pilot Plant, when again we ground the ore with three different types of grinding media. Incidentally, this has been the only pilot plant test made at the Mines Branch in which flotation products were made on both steel grinding and autogenous grinding on the same ore. The fourth part deals with two other New Brunswick ores and is intended to show that changing the grinding media effects ores other than that of Chester Mines Limited."

Jan 1, 1973

By Javier Linares García

At then end of this year will be 10 years of producing concentrate for Antamina. This is a summary of what occurred over the last decade to increase production and tonnage above the design tonnage of 70,000 tonnes per day, up to an average of 100,018 tonnes per day in 2010, an increase in production of 42.9%. Equipment currently in use is the originally installed equipment, signifying a meaningful increase in capacity without capital. In this paper, the different phases of improvements and the realization of their impacts in chronological order will be outlined. Figure 1 below shows the average daily tonnage processed each year (tonnage throughput each year/calendar days), as well as the percentage increase over the tonnage of design.

Jan 1, 2012

By Grant Small, Jessica Kinal, Christopher J. Greet

"The conversion from an electrochemically reactive grinding media (forged steel) to a more electrochemically inert alloy (high chrome white iron) not only reduces the wear rate of the grinding media, but also has an impact on the grinding chemistry. Typically the grinding chemistry becomes more oxidising, with less reducing Eh values and more dissolved oxygen in the pulp. There is also a decrease in the EDTA extractable iron, which is an indication of the change in the media corrosion. These changes are indicative of alterations in the surface chemistry of the minerals that the operator is trying to separate. For porphyry copper ores the changes in the pulp and surface chemistry not only affect the copper sulphide minerals, but also impact the iron sulphides (i.e. pyrite and pyrrhotite). Generally, with more oxidising pulp chemical conditions during grinding there is an increase in the oxidation of the iron sulphides which renders their surfaces hydrophilic, thereby depressing flotation. This leads to improved selectivity for copper sulphides against iron sulphides.INTRODUCTIONPorphyry copper deposits are the dominant source of copper that is mined today to satisfy global demand. These style of deposits typically contain one percent copper mostly as chalcopyrite, but may contain other copper bearing minerals (for example, bornite, chalcocite, azurite, malachite), small quantities of pyrite and quartz. Porphyry copper deposits also contain economically significant quantities of gold, silver and molybdenum. Interestingly, the majority of the world’s porphyry copper deposits are concentrated along tectonic plate boundaries (Figure 1)."

Jan 1, 2016

By P. Harvey

"Following initial discovery in 1991, BHP Billiton Diamonds Inc. opened Canada’s first diamond mine, the EKATI Diamond Mine (EKATI) in the Northwest Territories on October 14, 1998. Four short years later, on November 29, 2002, saw the opening of North America’s first underground diamond mine, the Koala North mine. Nestled between the original Panda open pit and the new Koala pit, which is in the early stages of production, Koala North represents the only underground kimberlite mining venture in Arctic conditions outside the new underground mines being developed by ALROSA in the Yakutsk region of eastern Russia. Extensive underground kimberlite mining has been practiced in the Republic of South Africa for much of the 20th century and continues today.Underground mining represents a key component of the long-term business plan for EKATI. As various open pits reach their economic limit, continued recovery of high-value ore at depth is dependent upon the ability to productively mine the kimberlite pipes by underground methods. As a function of its location, size, and value, the Koala North pipe is ideally positioned to host the first underground mine at EKATI. Koala North is designed and approved as a learning mine, from which to gain valuable experience in preparation for the potential mining of other larger, higher value pipes by underground methods in the development, the Koala North mine is well into its production ramp-up phase and currently producing at around 1,200 t/day from the first two production levels."

Jan 1, 2005

Background ArcelorMittal?s (formerly QCM?s) Port Cartier iron ore pelletization operations 2 side-by-side induration furnaces each producing 578 t/h of cured pellets Firing No. 6 fuel oil and coke breeze (in bed) Very large heat losses to be addressed primarily by gas recirculation

May 1, 2011

By Mauro Torres, Gabriel Zarate

"AngloAmerican used the extractant M5640 at Mantos Blancos and Mantoverde and uses PT5050MD at Los Bronces Division, which are aldoxime and modifier blends. In the first case, the modifier is the esther TXIB, while in the second case is the tridecanol TDA. It is a well-known fact that the extractant degrades while the modifier does not and with time the oxime/modifier ratio can change significantly, depending on the operating conditions of each plant.In order to evaluate the effect of this varying modifier content in the plant organic, especially in the organic losses, a complete metallurgical test work program was conducted at laboratory and pilot plant scale by Flomin SNF, a new extractant supplier. Results showed that the addition of an aldoxime without the modifier did not affect the chemical performance of the extractant, but there was a significant decrease in the viscosity and density of the organic.Based on the results obtained in the metallurgical program, it was decided to run plant scale tests at the SX plants of Mantos Blancos and Mantoverde. In these tests, instead of adding extractant to maintain the organic inventory, CuPROMEX 3406 which is an unmodified aldoxime was added until the original oxime/modifier ratio was reached. This was obtained after 6 months of operation and since then both plants are running with the extractant CuPROMEX 3302 both supplied by Flomin SNF.In the case of Los Bronces, the pilot plant work was completed and it is programmed to run similar plant scale tests. In this case, the oxime/modifier ratio increased and TDA will be added until reaching the original ratio.The plant results obtained at Mantoverde and Mantos Blancos, together with the pilot plant test results obtained at Los Bronces, are discussed in this paper."

Jan 1, 2016

By J. Lovering, M. Allan

"INTRODUCTIONThe Afton Mines property is located 180 air miles east-northeast of Vancouver and nine miles west of Kamloops, a city of 60,000 people in south central British Columbia. The deposit is located adjacent to the Trans-Canada Highway at an elevation of 2,231 feet above sea level.Interest in the property dates back to 1898, when a 330 foot shaft was sunk on the Pothook claim immediately south of the existing operations. Since that time many companies and individuals have investigated the possibilities of the area but it was not until 1972 that Afton Mines Ltd. located a significant zone of copper mineralization. The feasibility study was completed in the period 1974-1975, by Teck Corporation Ltd., who control Afton through 50% direct ownership and 65% ownership of Isa Mines, who own a further 23%. Construction began in March, 1976. Ore production started in August, 1977, and the first ore was fed to the mill on December 8. This was the third mine to be brought into operation by Teck since 1975, the others being Newfoundland Zinc and Niobec.The orebody is a porphyry copper deposit which has undergone supergene alteration. It is 1,700 feet long in a west-northwest by east-southeast direction, 300 feet wide and dips at 55° to the south. The mineralization in the supergene zone, which accounts for two-thirds of the known deposit, is rather unusual in that the copper is present primarily as native copper and chalcocite. The grade is one percent with the distribution: 70% native, 25% chalcocite, and 5% chalcopyrite with bornite, covellite, and cuprite."

Jan 1, 1979

By M. M. C. Lima, L. C. S. Solimani, M. A. Quintela

Galvanized steel scrap is recycled to B OF converters where zinc escapes from the bath and is captured by the gas control system, appearing in BOF sludge. As BOF sludge contain high iron content, it could be recycled, but due to its zinc content, it is disposed in landfills. In this study techniques were evaluated for zinc layer removal from scrap by sulfuric acid leaching. The effects of coating weight, temperature, time and sulfuric acid concentration were evaluated for three different galvanized scrap. The results showed that the behavior of each galvanized scrap was different. Nevertheless zinc removal efficiency was more than 80% with low dissolved iron in the leached solution.

Jan 1, 2011

By Martin Landwehr

"Dust samplers are based on different principles. The konimeter is based on the number of particles counted; mining applications are based on routine sampling; and the photometrical evaluation of samples is used after the pre-separation of particles above 5 micron by the mining konimeter. In special cases, the Draeger sampler is used for quantitative analysis. General trends are toward larger samples, concentration on a weight basis, fractionation into size groups by different techniques and an analysis of composition. Standards or TLVs already exist in all industries. Surface industries base their criteria on concentrations and quartz contents in particles below 5 micron. The mining industry uses the tyndalloscope routinely to determine concentrations; concurrent] y, the rock content, as deter-mined by ashing samples, is obtained by konimeter.Threshold limits are related to the rock content in respirable fractions and tyndallometrically determined concentrations. The TL Vs are based empirically on Landwehr's ""dust values,"" as agreed upon with the Mines Inspectorates. Recently, and in accurate sampling, dust samplers have been used that count the dust in two fractions -above and below 5 microns. Mineral composition is determined either for all minerais or just for quartz. In assessing the dust hazard by Landwehr's ""dust values,"" all minerais are taken into consideration; in coal dust sampling, however, only the quartz content is taken into account. Efforts are now being made to co-ordinate the different assessment methods, arriving at uniform MAC values in agreement with those of other countries."

Jan 1, 1969

By Tiziana Apuani

The study refers to an area of about 70 km2, extended in the Italian Central Alps along the the San Giacomo Valley where different civil and mining works are present The regional geological setting is related to the Pennidic Nappe arrangement, characterized by the emplacement of sub-horizontal gneissic bodies resulting from the Mesoalpine isoclinalic folding of crystalline basements, emplaced throw East, and separated by matasedimentary cover units. The investigated geological rocks, belong to the ?Tambò?Unit, overlapped by its meta-sedimentary cover and by the ?Suretta? Unit. The tectonic contact gently dips to the E?NE. The valley, furrowed by the Liro Torrent, follows a N?S striking tectonic lineament, almost parallel to the nappe contact. A number of more then 70 sites, distributed in the studied area, were chosen and detailed structural and geomechanical field surveys were performed to characterize the rock masses, its intact rock and discontinuities. The procedure identifies the number of joint sets, their representative orientation, the set spacing, the type of movement, the amount of dilatation, the degree of alteration, the roughness coefficient, the presence and nature of infill. Rock mass quality indexes, such as the Rock Mass Rating (Bieniawski, 1989) or the Geological Strength Index (Hoek et al. 2002) have been evaluated in each surveyed site. The work is a contribute in assessing how the geometrical and geomechanical properties of the rock masses can be regarded as regionalized variables. The spatial distribution of these properties is a function of the geological and structural phenomena at which the rock masses have been subjected. The presented geostatistical analysis regards the spatial variation of the orientation of the most representative joint set.

May 1, 2009

By Saravarim A.

"The aim in flotation systems is to control the grade and recovery of the product., numerical method or sampling and analysis is used to achieve this goal. Weakness of measuring instruments, lack of process knowledge, deficiencies in management and data processing in the control of flotation cells, has led the academic and industrial units to use numerical models. In this regard, using the results obtained from the experimental design carried out in the DTP line of Gol Gohar industrial and mining complex, a regression model was developed based on the analysis of variance. To present this model, after variance analysis of factors and interactions, all models were investigated and the final model was created based on 75% of the data. The model was tested with the remaining 25% of the data to confirm the goodness of the fit. The coefficient of determination for training and testing resulted 71% and 74%. Moreover, a feed forward back propagation neural network with different layers and neuron was used to model the results. The best network structure was 6-27-1 and the coefficient of determination for this network was 99% and 98% for training and test respectively. Given the complexity of neural network models and the relatively low accuracy of the regression model, neural network has a priority assuming we have access to a specialist. In addition, the results obtained from neural network can be used as expert systems to control and optimize the flotation cells.INTRODUCTIONThe primary objective of the flotation cell control is to maintain the product's (in this case tailing) recovery and grade, which represents the index for process efficiency and product quality. Continuous estimation of these indexes requires a significant amount of maintenance, and calibration of the continuous analyzers, in order to maintain an acceptable level of accuracy. Weakness of measurement equipment, lack of process knowledge and the general deficiency in management and processing of data in the flotation cell control, will lead industrial units to use smart methods such as mathematical models, regression and neural networks in near future (Panahi, Abdollahzadeh, & Sam, 2010). Artificial neural networks are inspired by the very complex structure of human brain in which millions of nerve cells solve problems or store information by communicating with each other. The duty of neural networks learning. It should be noted that learning in artificial neural networks is limited, and what is practically considered is the computing power of the network. A neural network consists of units called neurons, and has the capacity to handle a set of input data to produce a desired output data set. Each of these input and output data sets can be assumed as a vector (Soltanmohammadi & Noparast, 2006)."

Jan 1, 2016

By W. M. G. Heeley

In the province of Alberta the coal measures dip at so many different angles, between the horizontal and the vertical, that many different systems of haulage are in use. I will, however, only touch briefly upon the general -systems in use, and devote the major portion of this paper to a discussion of endless-rope haulage and its adaptibility to various conditions in coal mines; dealing in particular with the endless-rope haulage that was installed at Brule during the month of August 1923. In coal seams that are approximately level, and newly opened, hand-putting or tramming from the face is the cheapest, but when the mine is further developed tramming is out of the question, and the use of ponies is the next consideration. The time arrives, however, when mining reaches a point where the economical haulage of coal by horses cannot be done profitably, and then some system of mechanical haulage must be installed. The installation of any system should be carefully considered before any particular type of haulage is adopted, because a great deal depends upon the grade or dip of the seam. Motor haulage is impossible to operate profitably on a grade of over 6 per cent and, while it is possible to use ponies, on short runs, up to 9 per cent, some other means of main and secondary haulage must be installed when a 9 per cent grade, is exceeded. I will, therefore, deal first with secondary haulage, because even though a main haulage is established, secondary haulage can be used to feed the main haulage.

Jan 1, 1925

By Bernhard Schwab

A popular rule in the mining industry is that a property should only be developed if average unit production cost is less than a given proportion of the estimated long-run price of the mineral. This paper provides a comparative analysis of the average cost approach (ACA) with the use of net present value (NPV) as an investment criterion. It is concluded that the ACA is an easily understood and easily applied rule of thumb which may serve as a rough first screening device, for example in the early stages of deposit exploration. Its operational convenience is at the expense of accuracy and validity, and the NPV provides a sounder method of making decisions, especially in the case of marginal deposits.

Jan 1, 1978

By O`Donnell. P. J.

THE modern coal cutter is a highly developed, and to a certain extent a somewhat complicated, machine. The requisite power to cope with conditions as found must be generated by the motor with due regard to limitations in the matter of dimensions and weight. This imposes the necessity of relatively high speeds of rotation. Any factor external to the machine proper which tends to reduce the load on the motor and gearing is most important. Experience has proved that close attention to the question of cutter-chain details undoubtedly results, in practically every coal-cutting operation, in increased efficiency and reduction of power and maintenance costs. The chain is the unit of the coal cutter which most greatly affects the economical operation of the machine, and only by due consideration of conditions and by the proper selection of the right chain can best results be expected; also, intelligent care of the chain while in operation is essential if it is to give its best service. The chain is the part of the machine that carries the pick boxes or blocks, which are connected to each other by a pair of chain links. The power to drive the chain is trans-mitted by a sprocket. The chain runs in guides supported by a rigid member called a 'jib'. Figure 1 shows the various parts mentioned. The first requirement of a chain is that it cut the coal as fast as possible. The second is that it do so economically. Economy of cutting can conveniently be divided as follows: (1) Economy in power used. (2) Economy in pick life. (3) Economy ' in chain life. ( 4) Economy in jib life. (5) Economy in labour for maintenance.

Jan 1, 1936

By A. W. Jolliffe

AEROPROSPECTING may be defined as the application of the air view to the search for mineral deposits. The term is suggested as a preferable alternative to either aerial prospecting (which may be confused with areal prospecting) or air prospecting. The air view may be obtained by visual observation from an aircraft or by examination of air photographs; each has its particular advantages and disadvantages. Aeroprospecting should be regarded only as an aid to, and not as a substitute for, accepted prospecting methods ( l ). The Precambrian region north of Great Slave lake consists of two well defined physiographic units, a feature first noted by J. T. Wilson (2). The boundary between these lies close to the north shore of the east arm of the lake and extends northwesterly near Spencer, Beniah, Carp, and Ghost lakes (Figure 1). South and west of this line, exposed bed-rock makes up the greater part of the land area; eskers are very rare, and overburden is largely limited to rock-walled valleys and depressions. North and east of the line, outcrops are rare or absent, eskers are abundant, and most of the surface consists of drumlin-like drift hills, elongated parallel to the direction of ice movement (Figure 2). Where this boundary passes through the area shown in Figure 1, it lies near the 1,200-foot contour and may mark the maximum extent of the lake or sea arm present in this vicinity toward the end of the Pleistocene period. For convenience, the first area may be called the 'bed-rock belt' and the other the 'drift belt'.

Jan 1, 1945