ECONOMIC BESOUKCES. 521 



Detroit, in a small area that stands a little lower than the Detroit interlobate moraine, lake clays 

 are thick and furnish material for extensive brick works. In the Saginaw basin extensive 

 deposits of nearly pebbleless clay exist but are not drawn upon for commercial use so much as 

 the shales of that region. They are largely covered by sand deposits, so that their extent is 

 greater than might be inferred from surface exposures. 



On the borders of the Michigan basin lake clays are scarce, the eastern shore being prevail- 

 ingly sandy. At the south end of the basin, however, from the vicinity of Michigan City to 

 Hobart, Ind., some deposits of sufficient depth to be of commercial value are found. In the 

 Grand Traverse region in Michigan, in Antrim and Grand Traverse counties, extensive deposits 

 of clay or silt underh^ing the surface till have been utilized to some extent for brick manu- 

 facture, for which they are much more suitable than the overlying till sheet. They promise 

 to be a valuable resource and are accessible with very little stripping on the bluff-like borders 

 of the lowlands and lakes of the region. 



West of Rensselaer, Ind., in the Iroquois basin, which was covered by a small glacial lake, 

 lie silt deposits of considerable depth. These deposits are utilized by a brick plant at Brook, Ind. 



Many valleys formerly occupied by pools held in place by ice dams are filled to great depth 

 by silt deposits. Several such valleys are found in southwestern Indiana in Gibson, Pike, Vander- 

 burg, and Posey counties. 



In northwestern Indiana and southwestern Michigan, in many lines of drainage which were 

 obstructed by the Lake Michigan glacial lobe, silt deposits underlie the surface sands. Deposits 

 of this sort have been utilized in the clay industries at South Bend for more than 50 years. As 

 far back as 1859 1 extensive explorations were made to test the thickness of the clay. 



As the value of the clay for use in the industries depends on its freedom from objectional 

 ingredients and properties no statements concerning the importance of particular deposits can 

 be made. However, clay having but little stony material is found extensively, and no doubt 

 much of it will prove to have high commercial value. 



The clay deposits and clay industries of northwestern Indiana have been made the subject 

 of a special paper by Blatchley, 2 and the shales and clays of Michigan have been briefly discussed 

 by Ries. 3 On the whole, however, this resource, so far as these two States are concerned, seems 

 to have received scanty treatment in geologic literature. 



SAND AND GRAVEL. 



The many uses to which sand and gravel are put in the building trades and in road construc- 

 tion are making them a resource of far greater importance than was dreamed of a few years ago. 

 Even the drifting dune sand on the shores of Lake Michigan is being used in the manufacture of 

 sand brick and is shipped by the train load to Chicago for use in masonry. The gravel hills, 

 which a few years ago were considered useless by the farmer, are now in demand for road material 

 at a price per acre far above that of other farm land. 



The roads and road materials of Indiana are the subject of a report of more than 1,000 

 pages, 4 much of which deals with the occurrence of gravel and the use already made of it. It is 

 shown that throughout the area covered by the Wisconsin drift in Indiana suitable material for 

 road building is so widely distributed as to obviate all long hauls. Hundreds of miles of gravel 

 road have already been constructed. In southern Indiana some of the lines of glacial drainage 

 furnish extensive gravel deposits suitable for road building, but a more widespread source for 

 that part of the State is found in the rock formations, especially the limestone. 



In Michigan, sand and gravel are easily accessible in nearly all parts of the State. In some 

 of the more sandy parts the sand is so fight as to render the roads difficult to travel, and it has 

 been found expedient to stiffen the roadbed with a coating of clay. Gravel is less widely dis- 

 tributed than sand, and broad areas in the Saginaw basin and on the lake plains in the sou theastern 



i Indiana Geol. Survey, 1860, p. 200. 



2 Blatchley, W. S., Twenty-second Ann. Rept. Indiana Dept. Geology and Nat. Res., 1897, pp. 105-153. 



3 Ries, Heinrieh, Michigan Geol. Survey, vol. 8, pt. 1, 1900, pp. 1-66, especially pp. 48-62. 

 i Thirtieth Ann. Rept. Indiana Dept. Geology and Nat. Res., 1906, pp. 17-1057. 



