GEOLOGICAL SUEVEY OF THE TERRITORIES. 47 



with, scarcely an impetliment. But this subject will be treated more in 

 detail in subsequent portions of this report. We may, before describ- 

 ing the details of the geology of this district, enumerate the formations 

 we may expect to meet with. We have mentioned the existence of a 

 large thickness of the lake deposits, and, frequently covering them, 

 beds of basalt ; but still the latter, although a modern outflow, is not con- 

 fined to the vicinity of these Pliocene marls, but may burst up through 

 any of the rocks and overflow their surfaces. We are liable to meet with 

 them anywhere, and in most cases they ijredominate over all others. 

 The next group of strata older, are the coal-beds, which are exposed in 

 a break in the range, and aid in concealing the older rocks for an inter- 

 val of four or five miles, between the Canon and the Gallatin Mountains. 

 Then come a few obscure exposures, which are, no doubt, of Cretaceous 

 age, though no fossils were observed ; below them are well-defined Juras- 

 sic strata, and below these the quartzites and limestones of Carboniferous 

 age. None older than the. latter are exposed in this gorge. A few miles 

 farther to the southward, as well as to the northward, older rocks are 

 brought to the surface, and we find that the core of the mountains is 

 composed of granitoid rocks. 



Now, if we examine this range of mountains a little more in detail, 

 we shall find, as we enter the canon, a series of beds which are probably 

 Cretaceous, but dipping at various angles. In some portions of the 

 range, fragments of the beds are lifted up to the very summit, so far as 

 to form a broken arch. This arch is well shown on the north side of the 

 canon, while on the south side the two sides of the anticlinal terminate 

 in high jagged points of limestone, 1,000 to 1,200 feet above the plain 

 below. In the supposed Cretaceous beds no well-defined fossils could 

 be found, but in some beds of arenaceous limestone, were bivalves, which 

 I have no doubt are of that age. Below this group there is a series of 

 alternate layers of arenaceous olay, gray limestones, and sandstones, 

 with layers 2 to 4 feet thick, composed of an aggregate of broken shells, 

 with now and then a fragment perfect enough to be identified so as to 

 show their Jurassic age. Below these are some red sandstones and 

 clays, which might be remnants of the Triassic, and, as they contain no 

 fossils, any opinion about them is conjectural. I think, however, that 

 they are all Jurassic or Carboniferous. We then come to a great thick- 

 ness of Carboniferous rocks, first quartzites, gradually passing into lime- 

 stones. Rocks of Carboniferous age form the great mass of the minor 

 ranges of mountains. 



On the morning of July 12, a small party of officers from the fort, 

 under the guidance of Captain S. H. Norton, made a tour of exploration 

 to a little lake, embosomed among the mountains, about twelve miles 

 distant. We were accompanied also by Dr. Campbell and Lieutenant 

 Jerome, to all of whom we were indebted for many kindnesses and 

 much information. Our course was nearly south from the fort. After 

 passing over the beautiful grassy plain between the middle and east 

 borders of the Gallatin, we ascended the high hills on the west side 

 of the dividing range between the waters of the Yellowstone and 

 the Gallatin. These hills are so covered with debris and a heavy growth 

 of vegetation that not even in the ravines can the real basis rocks be 

 seen. On either side of us, however, in the very highest ridge, the 

 limestones are visible, with the reddish sandstones and clays, so that 

 we may infer that the Jurassic or Cretaceous are concealed beneath this 

 superficial drift. After winding among these hills, through a garden of 

 most beautiful wild-flowers, we reached the little lake, which, on account 

 of its great beauty, and being partially hidden, we called Mystic Lake. 



