GEOLOGICAL SURVEY OF THE TERRITORIES. 169 



series, 1 saw great quantities of fossils, among them several varieties 

 of Productus, Spirifer, &c, well-known carboniferous forms. Fossils of 

 the same age are quite abundant just over the range near Salt Lake 

 City, and in many other localities all over the valley. There may be 

 restricted areas in the Salt Lake basin where unchanged rocks of older 

 date than the carboniferous occur, but they have so far escaped my 

 observation, and we have no evidence of their existence from the ex- 

 aminations of other explorers. 



In my last preliminary report I alluded briefly to a series of sands, 

 sandstones, marls, &c, in the Weber Valley, between Morgan Station 

 and Devil's Gate, and also along the foot of the mouutains in Salt 

 Lake Valley proper. That they form a separate group from all others 

 I do not doubt, although in point of time they may be regarded as an 

 extension upward of the Wasatch Group. I have given these the name 

 of the Salt Lake Group, and I believe them to be of pliocene age. All 

 through the mountain districts these later pliocene deposits occur, com- 

 posed of light-colored clays, sands, marls, &c, not unfrequently yielding 

 numbers of vertebrate remains. The Salt Lake Group has so far revealed 

 but few fossils, only one species of Helix. During the middle tertiary 

 period, it seems probable that the metamorphic and granitic rocks 

 which form the nucleus of the mountain ranges were exposed to the 

 erosive action of the waters to a great extent, and thus their decomposi- 

 tion, mostly feldspar, supplied the materials for these pliocene deposits. 

 Their uniformity in composition and color is quite remarkable. Iu most 

 cases these beds have been very slightly disturbed and do not conform 

 to the older rocks, though I think they conform to the conglomerates. 

 These recent beds underlie the benches or terraces which form so 

 marked a feature in Salt Lake Valley. There are still more recent 

 deposits in Salt Lake Valley, which, from their magnitude, deserve 

 mention. As we emerge from the Weber Canon into Salt Lake Valley 

 we see on either hand high, rounded hills, which jut close up to the foot 

 of the mountains. All the older rocks seem to have been swept away, 

 leaving a very large area, from a point about ten miles north of Salt 

 Lake City to the mouth of Bear Eiver, occupied only by the arenaceous 

 clays of the quarternary period. The cuts along the railroad show 

 the character of these deposits quite clearly. Still more recent, 

 and probably forming a portion of this deposit, are the immense accu- 

 mulations of loose sands and drift or worn pebbles and boulders which 

 are found everywhere in Salt Lake Valley and extend high up the 

 valleys of the streams which empty their waters into Salt Lake. From 

 the mouth of Echo Creek to the Salt Lake Valley, Weber Valley is 

 covered with a prodigious quantity of worn rocks of greater or less size, 

 from a small pebble to boulders two or three feet in diameter. The 

 terraces are composed of line sediments, mingled with pebbles and 

 boulders. On the sides of the Weber Eiver, in its passage through the 

 Wasatch ra.age, we see fifty to one hundred feet of this fine sand, gravel, 

 and boulders, with a kind of irregular stratification, which indicates 

 deposition in moving waters. I mention these details to show with what 

 fidelity the records of the various changes, geographical and geological, 

 of this valley, have been preserved. We see that by careful examination 

 we can trace the history step by step far back, from the middle of the 

 tertiary period up to the present time. 



Let us for a moment glance at some of these intermediate steps and 

 ascertain what bearing they have on the progress of the growth of our 

 continent. The Salt Lake Group, which I have already described, I re- 

 gard as an important feature in the history. 



