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Mesozoic and Cenozoic Geology and Paleontology. 215 
ceaseless agency of water, not sweeping over the surface in the mighty 
currents of the diluvial epoch, bearing the detritus of northern crys- 
talline rocks, and grinding down and bearing away the softer strata, 
but falling as rain, percolating through the calcareous and magnesian 
deposits, and gradually carrying them off in solution, leaving the in- 
soluble portion behind, in the form in which we now see it covering 
the solid rock, as an intimate mixture of the finest argillaceous and 
silicious particles. 
The trunks and branches of coniferous trees, belonging, apparently, 
to existing species, are quite common in the blue clays at the base of 
the drift ; and in the brown clays above, the remains of the mammoth, 
the mastodon, and the peccary are occasionally met with. The fine 
fragment of a mastodon’s jaw, with the teeth, found at Alton, was ob- 
tained from a bed of drift, underlying the loess of the bluffs, which, at 
this point, was about thirty feet thick, and remained 7n situ above the 
bed from which the fossils were taken. Stone axes and flint spear- 
heads are also found in the same horizon, indicating that the human 
race was cotemporary with the extinct mammalia of this period. The 
bones and teeth of a great number of species are found in the crevices 
of the rocks in the driftless area of the lead region, where they have 
been washed from the surface, and carried in some instances fifty or 
sixty feet before finding a lodgment. The most abundant among the 
remains of animals thus found are those of the mastodon, whose teeth 
and bones have been procured from a great number of crevices, over 
the whole area of the lead region ; showing that the species must have 
lived and flourished in immense numbers, and through a long period of 
time, since the chances of the preservation of the remains of any one 
individual by being washed into a crevice, must have been exceedingly 
small. The remains of both living and extinct species are found in the ~ 
crevices in such positions, in reference to each other, as to indicate 
pretty clearly that they were living together. From a crevice, near the 
Blue Mounds, Prof. Worthen collected the bones and teeth of the masto- 
don, peccary, buffalo, and wolf—the two former extinct, and the two 
latter supposed io be identical with the living species. 
In 1867, Prof. C. A. White* found drift scratches upon limestone of 
the Upper Coal Measures, in Mills county, Iowa, near the Missouri 
river, having a direction 8S. 20° E., and these crossed by a finer set of 
scratches, having a direction 8S. 51° E. And at an exposure of the 
same limestone, one mile below Omaha, the capital of Nebraska, imme- 
* Am. Jour. Sci. and Arts, 2d series, vol. xliii. 
