DEKALB, KANE AND DUPAGE COUNTIES. 113 



from one to four feet of soil bearing large forest trees. It is exposed, however, 

 for a distance of several rods in the ditches alongside of the railroad track. 



The remains of extinct Post Tertiary mammals have heen found in the 

 superficial deposits in one or two localities in this district. A portion of the 

 remains of a Mastodon, consisting of the tusks and several teeth, were obtained 

 in excavating for the track of the Chicago, Burlington and Quincy railroad 

 near the City of Aurora, and are now preserved in the museum of Clark Semi- 

 nary, at that place. The skull, and it is said the other parts of the skeleton, 

 also, of Castoroides Ohioensis, were found by a farmer in a slough not far from 

 the town of Naperville, DuPage county. The skull was obtained by Col. Wood's 

 museum, in Chicago, where I believe it still remains. 



The deposits of the Drift, in this district, consist of loam and blue clays, 

 and hard-pan, with here and there, amid the mass, seams and pockets of sand 

 and gravel. Boulders of granite, quartzite, greenstone, and various other 

 rocks, are abundant in varions localities on the surface of the ground, and are 

 frequently met with in excavations for wells, etc., and large deposits of rolled 

 boulders, chiefly of limestone from the underlying Niagara beds, similar to 

 those already described in the report on Cook county, occur in the Drift de- 

 posits of the adjoining portions of Kane and DuPage counties. These may 

 be well observed in the vicinity of Elgin, and, in DuPage county, near Danby 

 and Bloomingdale. Sections of the bluffs in various places along Fox river, 

 show that the materials of the Drift have been rearranged, and present a strati- 

 fied appearance. The limestone boulder deposits may, perhaps, be referred to 

 this modified Drift. 



Pieces of wood, and occasionally large trunks and branches of trees, have 

 been found at considerable intervals in the Drift, and such cases are reported 

 in various parts of this district. At Sycamore, in DeKalb county, large pieces 

 of wood were said to have been met with, in the blue clays of this formation, 

 at the depth of fifty feet, in digging a well, and other instances were mentioned, 

 though no particulars were given. 



It is not easy to estimate the thickness of these deposits in all parts of this 

 district, as it is very seldom penetrated by wells or any artificial excavations; 

 nor is there generally in any such works any record kept of the materials, 

 which would also be very desirable in the study of this formation. The 

 bluffs along Fox river, however, furnish partial data for a portion of the dis- 

 trict, and, judging by these, the Drift will average from fifty to one hundred 

 feet in thickness, above the uppermost bed of rock. Away from the river, on 

 either side, the thickness is most probably not less, and may be even more. 

 At Sycamore, a well is said to have reached, by digging and boring, a depth of 

 (?) feet, without penetrating the blue clays and hard-pan of this for- 

 mation. 



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