66 Geological Socielt/. 



alluded to, but the same fossils have been brought from beds of the 

 Missouri and Yellow-stone rivers, as well as from their springs in 

 the Rocky Mountains j and they have been found west of that 

 range. 



Above the Big Bend occurs also an extensive range of horizontal 

 beds of lignite, sandstone, shale, and clay, forming bluffs 200 and 

 300 feet high, and continuous for several days' journey. Lignite is 

 also found on the Cherry River, and along the whole of the country 

 watered by the Powder River, in beds from 3 to 9 feet thick. This 

 formation Mr. Rogers conceives to be more recent than that which 

 contains the fossils, as the latter has a slight westerly dip, and there- 

 fore may underlie it. 



Silicified trunks of trees are stated to have been noticed on the 

 banks of the streams, and are considered by the hunters to have 

 fallen from the bluffs. 



No recent volcanic production appears to have been yet brought 

 from the country east of the Rocky Mountains, with the exception 

 of the pumice which annually descends the Missouri -, but nothing 

 is yet known of the quarter whence it is derived. West of the moun- 

 tains, however, from the Salmon River to beyond Louis's River, 

 and for a considerable distance around the insulated mountains 

 called the Butts, the country is said to be composed of lava traversed 

 by a multitude of deep, extensive fissures, having a general direc- 

 tion from north-west to south-east, and nearly parallel to that of the 

 mountains. 



Volcanic mounds, cracked at the top and surrounded by fissures, 

 are numerous over the whole region j but no lava appears to have 

 flown from them, and Mr. Rogers conjectures that they were 

 formed by the action of elastic or gaseous matter. In many places 

 deep circular funnels, a few yards in diameter, penetrate the sur- 

 face. For more than 40 miles the Columbia runs between perpen- 

 dicular cliffs of lava and obsidian, from 200 to 300 feet high, which 

 are traversed by great fissures, and present all the phsenomena of 

 dykes in the most striking manner. The Malador branch of the 

 Columbia flows through a similar gorge. 



In the course of the memoir Mr. Rogers corrects the account pre- 

 viously given of the great salt lake, which, he says, Mr. Sublette 

 journied round, and ascertained to have no outlet, though it receives 

 two considerable streams of fresh water. The length of the lake 

 is estimated to be 150 miles and its breadth 40 or 50. 



In conclusion, some observations are offered on the thermal springs 

 which abound along the base on each side of the Rocky Mountains, 

 and in the volcanic district. They are stated to vary in temperature 

 from blood heat to the boiling-point ; and to form, from their 

 earthy contents, large mounds, sometimes of a pure white, hard, 

 siliceous nature, and at others of a substance which on drying be- 

 comes pulverulent. In the volcanic district some of the springs are 

 said to be sour : and many sulphureous springs occur both in and 

 west of the mountains. Lastly, pure sulphur has been occasionally 

 seen above the Great Salt Lake, and at the eastern base of the 

 mountains, but none in the volcanic district* 



