| OCR Text |
Show 202 and Niobrara Rivers, are singularly alike, indicating their derivation ffon the same source. The metamorpbic rocks all over the West ' are com posed mostly of quartz and feldspar, the former predominating. It ii from the decomposition of these rocks that most of the Lacustrine sedi ments are derived. Judging from the character of the sediments, then were no yioleut currents in the channels of the streams in Lacustrim times, unless near their source. The sediments do not seem to diffe essentially in fineness where they lap over the flanks of the gnmit hills at the upper side of the basin. The fillingup of the basin also caused the channel above to be full, » that the fine matter would be distributed over the basin very equably and settle quietly at the bottom, as in any of oar small fresh- water lake of the present time. The thickness of the deposits in this basin inayb estimated at from 1,200 to 1,500 feet. The height of the divide betwee Madison and Gallatin Rivers ranges from 600 to 1,000 feet above th beds of those streams, so that it is probable that the estimate of th aggregate thickness as 1,500 feet is rather under than over the trn one. The writer was unable to find any of the vertebrate remains in tlii basin that, have usually been obtained from this formation in man other places. Many persons living in the country informed me the bad seen remains of turtles, fragments of skulls, and bones of oth< animals in various places, but the time at my disposal did not perm me to make a careful search. In the side gorges, or gullies, of the Mad son, we found most beautiful specimens of silicifled wood in great quai titles, some of which might be said to be opalized. In the valley of the Jefferson, near its source, there is one of thes small expansions of the valley, in which there is a considerable thicl ness of the Lacustrine sediments. In 1871,1 found there a species i Helix, and the jaws of a vertebrate animal of the genus Anchitheriut In the American Journal of Science for February, 1876, Messrs. Grii nell and Dana discovered a lake- basin near Camp Baker on Dry Creel which is evidently one of great interest In this basin they seem i have found a Variety of vertebrate remains, representing two epoch Miocene and Pleiocene. I am not aware that the lower beds of tl White River, group had been previously observed in Montana. It quite possible, as the gentlemen suggest, that the Pleiocene lake i Deep River was connected with those near Fort Ellis and the Thn Forks. We may, with perfect confidence, connect them all, for they ci be - traced with very short interruptions from the sources of the Madisc and Yellowstone Rivers and their branches to the points where tl rivers leave the mountain- districts for the plains. It may be I marked here that these peculiar Lacustrine deposits are found for tl most part only in the mountainous portions; that in the plains, if thi ever occurat all, they are of older date. In the valley of the Sweetwat River there are isolated patches of the Pleiocene marls distributed ov the Miocene deposits, very similar to those on Deep Creek; but there a here low granite ridges on either side, showing that the foundation-^ on which the modern Tertiary deposits were laid down in that regU is granite or gneiss. These same modern Lacustrine deposits occur the North and Middle Parks, Colorado. The lower section of Plate VII, » The Second Valley of the Yello stone,'' is an illustration of one of the oval Lacustriue basins so coi , r> ng the rivers. It is about thirty miles long, and. will averaj ^ e miles in width. The lake- sediments have been swept out to a great extent, but there are quite large remnants remai |
