144 GEOLOGICAL SURVEY OF THE TERRITORIES. 



that our eocene climate was warmer than the miocene, and that from the eocene epoch 

 to the glacial period a progression of temperature took place, the Green River beds 

 would seem to me to prove earlier than late miocene. 



Geologists have as yet explored this interesting region only in the 

 most superficial way, and we have caught but a glimpse of the wonder- 

 ful treasures which will some time be brought to light. The strata are 

 nearly horizontal, and the rivers have cut such deep channels in them 

 that they can be studied with comparative ease. Professor Denton, 

 who made an exploration of the country about one hundred miles south 

 of the railroad, has given a graphic account of his discoveries, which 

 shows very clearly the geographical extension of this formation. Near 

 the junction of White and Green Rivers, partly in Colorado and partly 

 in Utah, he describes an immense tertiary deposit, composed of a series 

 of petroleum shales, one thousand feet in thickness, varying in color 

 from that of cream to the blackness of cannel coal. The shales abound 

 in the impressions of leaves and of various species of insects. Mr. Sam- 

 uel H. Scudder, of Boston, published in the American Naturalist for 

 February, 1868, a most interesting account of the insects collected by 

 Professor Denton. He says : 



The masses of rock were crowded with remains of insects and leaves of deciduous 

 trees. Between sixty and seventy species of insects were brought home, representing 

 nearly all the different orders ; about two-thirds of the species were flies, some of them 

 the perfect insect, others the maggot-like larvae, but in no instance did the imago and 

 larvae of the same insect occur. The greater part of the beetles were quite small. 

 There were three or four kinds of Homeoptera, (allied to the treehoppers,) ants of two 

 diflerent genera, and a poorly-preserved moth. Perhaps a minute Thrips, belonging to 

 a group which has never been found fossil in any part of the world, is of the greatest 

 interest. 



At the present day these tiny and almost microscopic insects live among the petals 

 of flowers, and one species is supposed by some entomologists to be injurious to the 

 wheat ; others believe that they congregate in the wheat as well as in the flowers, in 

 the hope of finding food in the still smaller and more helpless insects which are found 

 there. It is astonishing that an insect so delicate and insignificant in size can be so 

 perfectly preserved in these stones ; in the best specimens the body is crushed and dis- 

 placed, yet the wings remain uninjured, and every hair of their broad but microscopic 

 fringe can be counted. 



Professor Denton also discovered in this region a deposit of petro- 

 leum coal, which appears identical with and would yield as much oil as 

 the Albertlte coal of New Brunswick. Another bed, resembling cannelite, 

 was noticed, ten to twenty feet in thickness, which Professor Denton 

 believes would produce fifty or sixty gallons of oil to the ton. If so, a 

 single bed here would yield twenty million barrels of oil, or a thousand 

 times as much as America has produced since petroleum was discovered 

 in Pennsylvania. It is clear that these shales, with the fossil insects, 

 leaves, and petroleum, are only a southern extension of the beds which 

 we have so fine an opportunity to study around the Green Elver Station. 

 Dr. Palmer has brought fresh water shells, as Goniobasls Carteri, and 

 others from White Eiver, which tends to strengthen this conclusion. 



From Bryan we pass over a peculiar region, differing again in its 

 surface features from any previously seen on our route. Far distant to 

 the southward the singular, dome-like appearance of what we have usually 

 styled the " bad lands" is visible, their brown and indurated sands and 

 clays having weathered into remarkable forms. One of these singular 

 hills forms a noted landmark along the old stage road, which has received 

 the name of " Church Buttes," from its supposed resemblance to a church. 

 To this formation I have given the name of the "Bridger Group," and 

 I am convinced that this region was occupied by a vast fresh-water 

 lake about the same time that the one on White Eiver existed. From 

 the indications derived from the fossil remains already discovered, this 



