HISTORICAL REVIEW 13 



"The question is, were the shells left in their present position by natural 

 agencies? To say that they reached their present position by natural means, 

 is to say that the waters of Lake Chicago at the Calumet stage were salt. This 

 would seemingly require the subsidence of this and surrounding areas to such a 

 level as would allow the incursion of the sea over this part of the interior of the 

 continent, and their subsequent elevation to the present altitude of 620 feet 

 above tide, within very recent geological time. 



"It is true that this is not the first or only suggestion of such a subsidence 

 and marine incursion. Dr. R. W. Ells 19 of the Geological Survey of Canada, 

 has recently brought forward evidence to show that the ocean extended west- 

 ward throughout the upper Ottawa basin in post-glacial time, leaving marine 

 deposits which are now 1000 feet above the sea level. Dr. Bell 20 also records 

 the presence of marine deposits north of Lake Superior, along the Kenogami 

 River, at an elevation of 450 feet above sea level. It is not unreasonable that 

 the subsidence of the area about Chicago should have occurred as a part of the 

 more general subsidence of which these marine deposits to the north and north- 

 east seem to be evidence. 



"The presence of the fossils mentioned above might be accounted for by 

 artificial introduction. They might have been thrown there by white men or 

 introduced in a fertilizer used on the soil. The well-known trading of the In- 

 dians of the northern interior with the south and east coast might account for 

 their having been left here, before the coming of the white men. They might 

 have been left on the beach of Lake Chicago by the Indians of that time, and 

 have been water-worn and buried by the waves of its shore. It should also be 

 noted that the physical relations indicate that the Calumet beach marks the 

 border of a lake which seems to have stood sufficiently above sea level to main- 

 tain a strong current through its outlet, which seems incompatible with the 

 occurrence of marine life in its waters. 



"On the other hand, the water-worn and fragmental condition of a large 

 part of the marine shells found on the Calumet beach, the thorough perfora- 

 tion of many specimens by sea-borers, the occurrence of very delicate, tiny 

 shells in the sand filling the coils of the larger gastropod shells, together with 

 the statements of Mr. Welch, that he himself cleared the ridge of its native 

 trees and underbrush, broke the sod, and has lived there for nearly thirty years, 

 that he never used any fertilizer containing shells, that the only evidence of 

 Indian residence he has ever found was a single arrowhead, that he has ploughed 

 up and gathered the shells ever since the ground was broken — all these facts 

 are against the idea of an artificial introduction of the shells, and favor the idea 

 of deposition in situ by marine waters. The southern range of all the species 

 found would also seem to preclude the idea of their introduction from the north 



19 Bull. Geol. Soc. Amer., IX, pp. 211-222, Feb. 1898. 

 " Report of Progress, Can. Geol. Surv., 1895, VI, p. 340. 



