OF WESTERN NORTH AMERICA. 



27 



or river-channel and flood-plain origin; for river-channel, backwater, 

 lagoon, and shallow-lake origin (Fraas) ; for flood-plain and eolian 

 origin (Hatcher, 1902") of various portions of these scattered deposits 

 (Darton) . 



Among paleontologists, Matthew (1899,^ 1901^) especially attacked 

 the lacustrine theory of the origin of the White River clay of Colorado 

 on both paleontologic and geologic grounds, and set forth cogent rea- 

 sons for a diametrically opposed eohan theory, comprising a river and 

 flood-plain origin for the sandstones, and a partly backwater and 

 lagoon but chiefly eohan sedimentation for the clays. His paleonto- 

 logic analysis shows that the fine Ohgocene clays contain chiefly the 

 terrestrial and plains animals and thus represent overflow and still- 

 water formations, while the sandstones traversing these clays are con- 

 temporaneous, but contain chiefly the forest and fluviatile animals, and 

 thus represent rapid-water (river) formations. 



The paleontologic evidence taken alone strongly favors the theory 

 of dry-land sedimentation of the so-called OHgocene clays, because the 

 entire fauna is terrestrial, while aquatic types are wholly wanting. 

 Thus Matthew ^ concludes in favor of an eolian theory : 



But the nature of the organic remains, where such have been found, seems to 

 definitely negative the idea of any vast lake, and to favor less the theory of a series of 

 lagoons and swamps than that of a broad, open, and comparatively dry plain, with shal- 

 low, probably wooded rivers meandering over parts of it, and deposits partly or chiefly 

 brought by rivers, but in large part redistributed over the higher sodded grass land by 

 the agency of the wind. This would mean an approximation to the present conditions 

 of climate, though probably not so dry as that of the region now is. 



Osborn,^ after a personal ^rvey of the South Dakota Oligocene and 

 lower Miocene section (see PL III) in 1906, in general supports the 

 view of Matthew and Hatcher that the lacustrine theory is entirely 

 untenable, but he holds that the eolian theoryfor the White River Oligo- 

 cene deposits is also untenable. The chief geologic evidence against 

 the eolian theory as applied to certain areas of the Oligocene or Brule 

 clay (Oreodon and Leptauchenia zones) is the absolutely regular horizon- 

 tal banding, miles in extent, which points to deposition in tranquil sheets 

 of water. In fact, this banding of the light-colored finer portions of 

 the Brule clay, and even of portions of the underlying Chadron forma- 

 tion, militates as strongly against the eolian theory as the paleonto- 

 logic evidence militates in favor of it. These buff, horizontally banded 

 strata are, on certain levels, abruptly traversed by grayish to greenish 



a Hatcher, J. B., Origin of the Oligocene and Miocene deposits of the Great Plains: Proc. Am. Philos. 

 Soc, vol. 41, 1902, pp. 113-132. 



b Matthew, W. D., Is the White River Tertiary an eolian formation? Am. NaturaUst, vol. 33, 1899 

 pp. 403-408. 



c Matthew, W. D., Fossil mammals of the Tertiary of northeastern Colorado: Mem. Am. Mus. Nat. 

 Hist., vol. 2, pt. 7, 1901, pp. 359-368 (conditions of deposition). 

 d Op. cit., 1901, p. 364. 



e Tertiary mammal horizons of North America: Bull, Am. Mus. Nat. Hist., vol. 23, 1907, p. 237. 



