254 UNIVERSITY OF COLORADO STUDIES 



certain broad valleys of the foothill and montane regions, while forests 

 are present on the hillsides there are only a few scattered trees on the 

 level ground below. This absence of trees is probably to be accounted 

 for by the fineness of soil and greater severity of climate. 



Colorado forests in former geologic times. — Professor T. D. A. 

 Cockerell, the authority on fossil plants of the Rocky Mountains, has 

 recorded a large number of species of trees which formerly grew at 

 Florissant and at other places in Colorado. The most easily accessible 

 of his papers are referred to in a footnote. * It appears that the forests 

 of Miocene times were made up of pines, cedars, willows, cottonwoods, 

 birches, alders, oaks, hackberries, June berries, thornapples, locusts, 

 sumacs, maples, buckthorns and ashes, besides a number of eastern 

 and southern trees which do not now exist in the state at all. Among 

 these others were: mulberry, soapberry, acacia, redbud and walnut. 

 No doubt the climate was much warmer at that time and, in the 

 mountains at least, more moist. The fossil remains of many of the 

 leaves are very perfect and the trees can be told with considerable cer- 

 tainty. We may be sure that for thousands and perhaps millions of 

 years the pines, cottonwoods, cedars and thornapples have been an 

 important part of the vegetation of this part of the world. 



Literature dealing with Colorado trees. — The well-known manuals 

 of botany of the eastern United States such as Gray's and Britton's, 

 describe certain of the tree species of Colorado. So, also, the Rocky 

 Mountain Botany 2 by Professor John M. Coulter, issued many years 

 ago, gives descriptions of a part of the arborescent flora of the state. 

 Unfortunately there is no new work which gives all of the trees nor one 

 which discusses the forest formations. Probably the most useful single 

 book is the new work of Dr. Britton. 3 Anyone interested in the larger 

 aspects of forestry will find useful articles from time to time in the 

 National Geographic Magazine and in the magazine, Conservation. 



1 Cockerell, T. D. A. "Florissant; A Miocene Pompeii," Popular Science Monthly, Vol. LXXIV, 

 pp. 112-126, 1908. "Some Results of the Florissant Expedition of 1908," American Naturalist, Vol. XLII, 

 pp. 569-581, 1908. 



' A new edition of this work, rewritten by Professor Owen Nelson of the University of Wyoming, is to 

 be issued in 1910. 



3 Britton, N. L., North American Trees, pp. 1-894, New York, 1908. 



