662 GEOLOGICAL SURVEY OF THE TERRITORIES. 



features of the country surveyed by us this year, I will refer you to the 

 first pages of the geological report of Mr. A. E. Marvine, where he has 

 given all that can be said on the subject. 



The district surveyed may be divided into three natural areas, sepa- 

 rated by the line formed by the eastern edgeof the mountains where the 

 sedimentary beds are upturned against the metamorphic rocks, forming 

 the ridges known as the Hog-backs ; and by the line of the main water- 

 shed of the continent. The Hog-backs make a sharp line of demarka- 

 tion between the plains and the mountains ; the plains being essentially 

 destitute of timber, except a growth of cotton woods and willows along 

 the streams. 



The central mountainous portion, drained by Big and Little Thomp- 

 son Creeks, Saint Vrain's Creek, Bowlder Creek, Clear Creek, and 

 Bear Creek, with their numerous branches and forks, all of which are 

 tributaries of the South Platte Eiver, contains about 1,700 square miles. 



The ridges and mountains are well timbered, mostly with the yellow 

 and white pines, Finns ponderosa and AMes Engelmanni, and the parks 

 and valleys bear a fine growth of scattered timber. 



In the vicinity of the mining towns a great deal of the timber has 

 been cut, and in places over large districts it has been destroyed by fire ; 

 1,200 square miles of this section is timber-bearing, the remainder being 

 either above timber-line or else taken up in the open valleys and parks. 



The western division, including the Middle Park, contains about 2,025 

 square miles, all of which is drained by the Grand River and its tribu- 

 taries. This area may be divided into timber, grazing and farming, or 

 bottom lands. 



The spurs thrown out from the main range which surrounds the park 

 on the north, east, and south, and the ridges and mounlain masses form- 

 ing the divides of the principal streams, are well timbered, especially in 

 the eastern half of this section. 



The relation between the geological formations and the growth of 

 timber is very interesting. There is apparently a greater change from 

 this cause than that due to difference in altitude. 



The hills formed by the metamorphic rocks, wherever they occur, ex- 

 cept above timber-line, grow good timber, mostly white pine, although 

 on western slopes it is smaller, and therefore of poorer quality than on 

 eastern. The amount of this granite-timber area is about 675 square 

 miles. 



The lignitic areas, which comprise a large portion of the park, as the 

 Williams Mountains, and the greater portion of the country drained by 

 the Willow, Corral, and Troublesome Creeks, are essentially timber-re- 

 gions ; but the quality of the timber is very inferior to that growing on 

 the metamorphic rocks, and the southern slopes are generally bare. 



Over large areas the timber has fallen, making it often difficult to 

 travel away from the trails. This class of timber-land might be esti- 

 mated at 425 square miles. 



The regions covered by the lake-beds are, as a rule, totally destitute 

 of timber. 



The areas covered by Cretaceous No. 1 bear timber, while the remain- 

 der of this formation, usually occupying the lower valleys and partially 

 covered by the lake-beds, does not represent a timber-country. This is 

 illustrated in the valley of the Blue, where the timber-growth follows 

 the outcrop of Cretaceous ]S"o. 1 across the valley. This class covers 

 about 150 square miles of country. 



The hills capped with lava grow timber. All told there are about 1,250 

 square miles of timber-land in this western subdivision. 



