12 THE CHICAGO ACADEMY OF SCIENCES. 



the waters now nearly filling the old Stony Island Quarry 

 (PL VIII, fig. 2) he would have difficulty in believing himself 

 near Chicago. Yet so uniform are the strata in general that the 

 region is devoid of metamorphic phenomena, and the variety 

 of its mineral types would have been extremely limited were it 

 not for its emigrants. Throughout the greater part of the re- 

 gion, the Niagara limestone, as is well known, is buried under 

 a cover of clay, sand, and gravel, in places more than 2CO feet 

 thick. The source of much of this material has been discov- 

 ered by comparison of boulders with Wisconsin, Michigan, 

 and Canadian rocks. That the larger part of it has been 

 transported but a short distance can be made evident in a 

 number of ways. Four men working about thirty minutes on 

 the lake shore at the University campus at Evanston, collect- 

 ing the rocks from a pile of gravel about eight feet square, 

 sorted them into five groups. PI. I shows the result. The 

 pile of limestone is in bulk somewhat more than twice that 

 of all the other piles put together. The pile of chert is more 

 than twice the volume of the three remaining piles united. 

 The acid granitic rocks and the gabbros and diabases are about 

 equal in volume, while the metamorphics play a very insignifi- 

 cant role, being hardly visible in the photograph. These 

 results agree with those obtained by the writer at various 

 by points along the lake shore, and accord with estimates given 

 Leverett (Leverett, Pleistocene Features of the Chicago Area; 

 Chicago Acad. Sc. Bull. 2, p. 49, et seq.) Results that point in 

 the same direction are obtained by taking a gramme of sand 

 and dissolving it in various acids in succession. Hydrochloric 

 acid (hot) dissolves out the carbonates and iron oxides; some 

 of the silicates (anorthite, hypersthene, serpentine); some 

 phosphates (apatite); some sulphates (gypsum). The results 

 of five analyses show 16% of such minerals soluble in 

 hydrochloric acid. Hot sulphuric acid which would re- 

 move fluorite, zircon, biotite, takes away but 0.4 % of the 

 original mass; showing the unimportant role which these 

 minerals play. Finally, of the minerals unattacked by the 

 above acids and yet soluble in nitric acid (most of the metals 

 occuring uncombined and the sulphides of which the greater 

 part is represented by marcasite and pyrite) there are 1.35% 

 in sand. Thus we have remaining 82% of material insoluble 

 in the strongest acids. It is chiefly quartz. A by no means 

 inconsiderable portion, however, is formed by rutile, garnet, 



