CHAPTER XXVI. 



ECONOMIC RESOURCES. 



By Frank Leverett. 



Only deposits of economic value connected with or developed upon the formations which 

 form the theme of this monograph are discussed in this chapter, and as special reports have been 

 published by this Survey and by the State surveys on the more important of these economic 

 resources, the discussion aims merely to direct attention to these reports and to set forth in a 

 very general way the relations of the resources to the glacial formations. 



ERRATICS IK THE DRIFT. 



In the drift are incorporated metals and ores such as copper, iron, and gold, precious gems 

 like the diamond, and blocks of coal, whose sources are in the rock formations passed over by 

 the ice sheet. (See pp. 64, 249.) All these are so rare and so irregularly distributed that they can 

 not be profitably worked on any commercial scale, but are to be classed as ' 'finds." Gold wash- 

 ing has, it is true, been attempted at a number of places in Indiana and neighboring States, but 

 has scarcely ever yielded a fair day's wage and can be said to pay only when the mi ners have 

 leisure time to spend. Before the character and origin of the glacial deposits were understood 

 the finding of these metals and gems led to erroneous conclusions as to their occurrence in paying 

 quantities in the near vicinity, and conclusions of this sort are drawn nowadays by many 

 irninformed persons. 



In some localities, where the rock formations are completely covered, the glacial deposits 

 contain sufficient amounts of certain kinds of building stone in the form of bowlders to consti- 

 tute a valuable economic resource, which, though becoming scarce in many localities, will not be 

 exhausted for some time. Such stone is especially plentiful along most of the moraines. In 

 other places masses of limestone have been so abundant in the drift or on its surface that they 

 have supplied limekilns for years and have been very useful, especially in the early days of 

 settlement. 



MARL OR BOG LIME. 



Marl deposits of great depth, sufficient to warrant the erection of large cement mills, exist 

 on the borders of many lakes of Indiana and Michigan. These deposits were drawn on by early 

 settlers for lime and to some extent for land plaster. Their use was so extensive and their value 

 so great that in the earliest surveys of both States data were collected as to their distribution. 

 It was not, however, until they began to be used on a large scale in the nianuf acture of Portland 

 cement that special reports on them were prepared. In Indiana the State Geological Sur- 

 vey has made systematic investigation of nearly all the lakes and basins which formerly held 

 lakes but are now filled with marl and peat. The published report sets forth not only the extent 

 of workable but also of what are classed as unworkable deposits, the latter term being applied 

 where the quantity seems insufficient to justify the erection of a cement mill. 



In Michigan the investigations have been less complete. The field, however, is much more 

 extensive than in Indiana, for marl lakes are scattered over the whole of Michigan and they 

 occupy only a small area in the northern part of Indiana. The mills for the manufacture of 

 Portland cement in Michigan, however, are nearly all located in the populous southern part, 

 where a strong demand for the product exists, where transportation facilities are good, and where 

 the clay or shale needed in the manufacture of cement can be had within convenient distances. 



519 



