GEOLOGY. 257 



it has a source fax* in the north oi' north-west, beyond Lake Supe- 

 rior, and beyond the Mississippi, perhaps away off in the Rocky 

 Mountains. — Mechanics' Magazine, Feb., 1866. 



MINERAL RESEMBLmG ALBERTITE, FROM COLORADO. 



Prof. William Denton, when on an exploring trip west of the 

 Rocky-Mountain Range, in July, 1865, found, near the junction 

 of White and Green Rivers, a series of tertiary beds of brown 

 sandstone, passing occasionally into conglomerate, and thin beds 

 of bluish and cream-colored shale alternating with the sand- 

 stones. 



These beds dip to the west at an angle of about 20° ; and, cropping 

 out from beneath them on the east are beds of petroleum shale, 

 a thousand feet in thickness, varying in color from a light cream 

 to inky blackness. One bed, ten feet in thickness, which he traced 

 for six miles, is scarcely distinguishable from the best cannelite 

 of New Brunswick. In the sandstone overlying the shales, he 

 found a i^erpendicular vein of bitumen, resembling in lustre, frac- 

 ture, and other physical characters, pure Albertite. This vein has 

 a width of from two feet six inches, to three feet four inches; it 

 lies between smooth walls of sandstone, and was traced for a 

 distance of five miles in a nearly direct line, due west. Two 

 more small veins were discovered parallel to the first, one south, 

 and the other north, and each distant about a mile. 



The sandstone has been eroded by water into ravines and caii- 

 ons to a depth of from eight hundred to one thov;sand feet, and 

 the pi-incipal vein can be traced from the tojj of the mountain to 

 the bottoms of these canons, retaining its width, but not appar- 

 ently increasing it. In the sandstone he found fossil wood of 

 deciduous trees, fragments of large bones, most of which were 

 solid, and tuitles, some of which were two feet in length, and 

 perfect. The sandstone is proljalsly of Miocene age. 



In the petroleum shale, underlying the sandstones, are innumer- 

 able leaves of deciduous trees ; among them he thought he recog- 

 nized the willow, the maple, and the oak. Dipterous insects, 

 resembling the musquito, and their larva?, abounded ; they are in 

 a wonderful state of preservation. 



The story that these beds tell seems to be this : A large fresh- 

 water or brackish lake existed, covering a considerable portion 

 of western Colorado and eastern Utah. Streams carried down 

 fine sediment and free petroleum, from numerous springs in the 

 surrounding country, for ages ; the petroleum increased in flow 

 until the sediment of the lake became thoroughly charged with 

 it, and the cannelite was the result. A change in the level of the 

 country and the course of the streams is indicated by the overly- 

 ing sandstones and conglomerates, nearly destitute of petroleum, 

 and at least one thousand feet in thickness. During the time that 

 this immense amount of sediment was being deposited, willows, 

 maples, oaks, and many strange trees grew on the land, palaeo- 

 theres and turtles swam in the waters, and clouds of insects 

 sported over its surface. The bitumen seems to have flowed from 

 22* 



