6 Zoology of Colorado 



might pass for a different species, but for the occasional presence 

 of a blue-flowered plant. Steep trails lead up the mountain side, 

 or one may climb arduously up the shifting rock-slopes, to arrive 

 at the top very short of breath. The tops of these mesas afford a 

 splendid view of the surrounding country, but at certain seasons 

 of the year the traveler is unmercifully persecuted by biting flies 

 (Symphoromyia), blood sucking members of a group (Rhagionidae) 

 which is otherwise quite inoffensive. 



Some distance below the highest levels, or on the summits of 

 the partly eroded spurs, we find a rather thick layer of dense gray 

 rock, which will burst into flame on being placed in the fire. This 

 is the famous oil shale, which will, in case of need, supply almost 

 unlimited quantities of petroleum. In many places assessment 

 holes have been blasted and dug, as though gigantic gophers had 

 been burrowing in the mountain side. These excavations, costing 

 large sums of money, furnish the paleontologist's opportunity. 

 Here he finds great piles of the shale, which he has only to turn 

 over or split in order to discover remains of plants and insects, 

 sometimes beautifully preserved. The age is Eocene, in the 

 earlier part of theTertiary, and the particular division of the Eocene 

 represented is known as the Green River. This last name is 

 derived from the locality Green River, Wyoming, where beds of 

 this period were first carefully studied. In Wyoming, at certain 

 places, there is an amazing variety of beautifully preserved fish 

 skeletons, which are often prepared as neatly trimmed slabs, and 

 sold to visitors. In the Roan Mountains such fishes have not 

 been observed, though polished ganoid scales of a kind of garpike 

 (Lepidosteus) occasionally occur. This is a freshwater animal, 

 and indicates freshwater conditions, though it is by no means 

 certain that there were not saline lakes, into which freshwater 

 organisms, or portions of them, were carried from rivers. We 

 have not found any mammal bones in the oil shales, but it is a 

 very extraordinary circumstance that maggots of a kind of bot-fly 

 (Lithohypoderma ascarides) are exceedingly abundant over a very 

 wide area, at a certain level. We can only suppose that these 

 were parasitic on some mammal of the period, but at present the 

 matter cannot be further explained. There is no doubt as to the 

 nature of the maggots. Occasional feathers in the shale testify 

 to the presence of birds. Sometimes these are ordinary small 



