72 GEOLOGICAL SURVEY OF THE TERRITORIES. 



at Table Bock and Bed Desert, and on the old stage road at Big Pond 

 and La Clede, were taken from these shell beds. These layers of rock 

 extend over hundreds of square miles, and all the buildings for large 

 cities might be constructed from the aggregate remains of these little 

 fresh-water animals. Marine limestones of great thickness, composed 

 entirely of organic remains, are not uncommon in various portions of 

 our own county, but I have never known such extensive beds of rock 

 made up entirely of a few species of fresh-water shells. At the present 

 time both fresh-water and land shells are very rare in this country ; 

 the physical conditions seem to be very unfavorable, except at the 

 sources of some of the tributaries of the Missouri Biver that come in 

 from the north, as the James, Vermillion, and Big Sioux Bivers. These 

 streams are filled with Unios, Yiviparas, Lymneas, Planorbis, Physas, 

 &c. ; and yet the conditions seem to have been more favorable in years 

 past for this kind of life than at present. In the fine vegetable matter 

 that accumulates along the Missouri Biver from the annual floods, I have 

 seen bushels of minute Helices, Pupas, Succineas, &c, and yet I have 

 looked in vain for any of these shells alive in the little streams in the 

 vicinity. In the banks of the streams that flow into the Lower Missouri, 

 as Big Sioux, Vermillion, and others, large accumulations of fresh- water 

 and land shells are found buried fifteen to twenty feet beneath the sur- 

 face ; yet it seems to me, that if all that have ever existed in this region 

 were gathered together, they would not cover a large area. In the Mis- 

 souri Biver, from the base of the mountains to its entrance into the 

 Mississippi, scarcely a shell can be found, and very few ever are seen in 

 any of the branches that flow in from the south. The inference is, that 

 the impurity of the waters over the greater portion of the West is such 

 at the present time that this class of life cannot exist. How favorable, 

 then, must have been the conditions for the increase of molluscous life in 

 these old tertiary times! Not only were the waters pure, but through- 

 out all the vast thickness of middle and upper tertiary deposits in the 

 beds of clay and sandstones, there is more or less calcareous matter, as 

 is shown by the application of an acid ; proving that lime, which is so 

 essential to these animals, must have existed in the waters of that period. 

 About six miles east of Big Pond Station, a well-marked bed of reddish 

 clay is exposed, which can be seen extending across the country, over 

 the sides of the bluff-like hills, for many miles. I call attention to 

 this red band of clay, from the fact that it seems to mark the appear- 

 ance of the lower portion of the middle tertiary, and increases or dimin- 

 ishes in importance in different localities. On the east side of Green 

 Biver, opposite the mouth of Henry's Fork, these clays, with a reddish 

 tinge and bands of light brown, reach a thickness of one hundred to one 

 hundred and fifty feet, and weather into quite regular and picturesque 

 forms. 



On the west side of the South Pass these light-red clays are well dis- 

 played near the base of the middle tertiaries, and in some calcareous 

 layers above them are multitudes of fresh-water shells. This band is 

 also seen at the eastern terminus of the Green Biver group, near Bock 

 Springs, and near the sources of the Muddy west of Bridger's Pass. It 

 also gives name to the station on the Union Pacific Bailroad, "Bed Des- 

 ert," from the fact that the contiguous hills receive their color from it. 



Whether these formations are connected geographically or chrono- 

 logically with the vast series of red beds west of the eastern rim of 

 the Great Salt Lake Basin, a more extended exploration must determine. 

 The shell beds lie above this in all the localities that I have examined 

 except near the South Pass, where a bed of very porous sandstone 



