SUEVEY OF COLOEADO AND NEW MEXICO. 15 



were undoubtedly synchronous, tLough perhaps not connected with this 

 great basin. Every year, as the limits of my explorations are extended 

 in any direction, I find evidences of what appear to be separate lake 

 basins, covering greater or less areas, and bearing intrinsic proof, more 

 or less conclusive, of the time of their existence. I have given in this 

 place the above brief description of the various geological formations 

 as 1 have studied them in the West, in order that my subsequent remarks 

 on these formations in their southern extension may be more clearly 

 understood. Constant reference will be made to rocks as they have 

 been seen in the far North and West, in order that the story of their 

 geological extension may be linked together. 



June 29, 1869. — Left Fort D. A. Eussell about 10 o'clock in the morn- 

 ing with my entire party, consisting of twelve persons and eighteen 

 mules and horses, with two large covered wagons and an ambulance. 

 By the kindness of Colonel E. B. Carling, the depot quartermaster, at 

 Fort D. A. Eussell, I was provided with everything needful for inde- 

 pendent camp life, and I at once commenced my explorations in earnest. 



We traveled to-day thirteen miles southward from Fort Russell. Our 

 entire route was over the more recent beds of the White River tertiary 

 basin. The lowest bed exposed by the cuts in the streams, is a thick layer 

 of flesh-colored indurated marl, much like that containing so many ver- 

 tebrate fossils on White River, Dakota. It contains some thin layers of 

 very fine gritty rock. Overlying this is a thick bed which appears more 

 recent, yet apparently conforms to the marl beds below. It is composed 

 of water-worn pebbles of yarious sizes, forming a real pudding-stone. 

 ]S"ear the margins of the mountains this bed gives the characteristic 

 features to the scenery, as it is cut through by the myriad small streams 

 that issue from the mountain side. It is at least three or four feet in thick- 

 ness. Most of the pebbles are from the granite rocks that form the cen- 

 tral portions of the Laramie range. The beds all dip from the mountains 

 eastward at a moderate angle, and it is evident that this entire forma- 

 tion was deposited after the mountain ranges had nearly reached their 

 present height. The strata seldom dip at an angle of over 5° and rest 

 unconformably on the older beds when they are seen in apposition. 

 Near the junction of the metamorphic rocks with these modern pud- 

 ding-stones the pebbles or bowlders are not much worn, and of mode- 

 rate size, six to twelve inches in diameter, but the sediments grow finer 

 and finer as we recede from the foot of the mountains until the pudding- 

 stones pass into a fine grained whitish sandstone. We can see, therefore, 

 that these deposits formed the proper rim of the fresh-water lake, that 

 the sediments were derived from the erosion of the feldspathic granites, 

 and that the forces that were in operation acted from the direction of 

 the mountain ranges. 



There are also vast quantities of drift material which I regard as local. 

 It seems to me that the evidence is clear that all this modern drift-action 

 had its origin in the mountain ranges in the immediate vicinity ; that in 

 earlier times the snow and ice gathered on the summits in vastly greater 

 quantities, and that in melting, from year to year, in the form of water 

 and ice, they brought along vast quantities of rocks from the mountains 

 and distributed them over the surface. 



The waters, with the masses of ice, would naturally follow the chan- 

 nels of the streams if they had been marked out, or they would mark out 

 new channels, for nearly or quite all the valleys that extend down from 

 the mountains become shallower, the further they extend eastward from 

 the flanks of the range. This superficial deposit at the very margins of 

 the mountains is composed of very coarse materials, sometimes immense 



