GEOLOGICAL SURVEY OF THE TERRITORIES. 133 



favoiecl in regard to light and warmth passed apparently through the entire trans- 

 formation in about twenty days, those which commenced at the same time, but were 

 less favorably situated, required at least twice that time for its completion. The only 

 living specimen still remaining unchauged has twice shown slight indications of an 

 approaching metamorphosis, but with the exception of some spots, these have appa- 

 rently soon disappeared after a transfer to a dark and cooler place. 



As we pass on westward we come into the eastern border of the great 

 coal fields of the Rocky Mountains, and inasmuch as they are of vast 

 importance to this great thoroughfare, as well as to the country, I will 

 make them the subject of the next chapter. 



CHAPTER XL 



WESTWARD TO BEAR RIVER. 



Soon after passing Medicine Bow Station, the dark, somber appear- 

 ance of the surface of the country ceases, and the more cheerful aspect 

 produced by the overlapping of the tertiary beds is seen. We move on 

 rapidly through inclined ridges of sandstone and shaly clays, clipping 

 westward from 30° to 50°. Here we begin to discover indications of 

 coal in the black bands of carbonaceous clay that crop out on either side 

 of the road. But the most marked development of the coal beds will be 

 observed at Carbon Station, about one hundred miles west of Laramie. 

 The first openings were made about three hundred yards from the rail- 

 road track, where a bed of coal was discovered nine feet in thickness. 

 The demand for the coal was such that it was thought advisable by the 

 company to sink a shaft close by the track, and now the coal is taken 

 out in large quantities daily for the use of locomotives. A thriving little 

 town has been built up here by the coal trade alone. 



The coal which is taken out of this mine is of the best quality of the 

 tertiary brown kind, and is very compact and pure. It is not as hard 

 as anthracite, but the miners informed me that it was more difficult to 

 work than the bituminous coals of Pennsylvania. The engineers speak 

 in high terms of it as fuel for locomotive use. 



Just over the coal is an earthy bed of what the miners call " slate," 

 which breaks into slabs, showing a woody fiber, and much of it looks 

 like charred wood or soft charcoal. A little higher up we find thin 

 layers composed almost entirely of fragments of deciduous leaves, and 

 above these come various kinds of clays and sands. Beneath the coal 

 there are indurated clays and rocky strata, in which occur thousands of 

 impressions of leaves much like those of our common forest trees, but 

 belonging to species long since extinct. They belong, however, to 

 genera such as Populus, Platanus, Tilia, with many others, most perfectly 

 preserved, and all plainly pointing to a period far back in the geologi- 

 cal past when these vast, treeless regions of the present time were cov- 

 ered with dense forests, surpassing even those now growing in Ohio and 

 Kentucky. Some of the layers of rock, two to four inches in thickness, 

 are almost entirely made up of these leaves, and the condition in which 

 they have been preserved shows that they could not have been trans- 

 ported any distance, but must have fallen from trees that grew in the 

 vicinity. Indeed, there is no doubt, for myriads of ages in the past, 

 gigantic poplars, sycamores, lindens, oaks and others spread their 

 broad branches over the shores of some little streams or lakes, and shed 

 their foliage in the shallow waters in the same manner as they do at the 

 present day. In the autumn I have seen the sandy bottoms of the little 



