LETTER TO THE SECEETAEY. 5 



understood that both in quantity and quality, this coal improves. In 

 the southeastern portion of the district, above the Grand' and Eagle 

 Eivers, the sedimentary rocks, from the extreme base of the Cretaceous 

 down to the granite rocks of the Park range, occur, all thrown into a 

 series of complicated and peculiar folds. Limestone occurs near the 

 Grand in abundance, and on both the Grand and Eagle Rivers are great 

 deposits of gypsum, though other economic products, except some salt 

 and soda springs, will probably not be found here. 



The imposing mesa about the head of White River and several larger 

 areas near the Park range are composed of great floods of volcanic 

 rock, which have poured over the country in comparatively recent times, 

 bat some of which are yet old enough to have experienced the vicissi- 

 tudes of the Glacial period of the West, and to have received a profound 

 impress from erosion, similar to that now going on over the whole 

 country. 



The topographical work of the party under my immediate direction 

 was intrusted to Mr. G.B. Chittenden, and was divided into three parts : 

 first, the mapping of the peculiar features of the morainal deposits in the 

 Upper Arkansas Valley; secondly, the reworking of the topography of the 

 Elk Mountains on a larger scale, and with more detail than was possible 

 during the preceding season in the regular progress of the survey ; and, 

 finally, the laying down of the topography, and the line of junction of 

 the metamorphic and sedimentary rocks, and also the coal-outcrops on 

 the eastern base of the mountains, from Canon City to the northern 

 boundary of the Territory, making, in this latter division, small detailed 

 maps where points of particular interest or peculiar complication made 

 them seem desirable. In pursuance of this plan, the work began at 

 Colorado Springs, in order to investigate that region in detail, before 

 the main party would be ready to proceed across the South Park to the 

 work in the west. Forty-five topographical stations were made on the 

 sedimentary rocks, within ten miles of the springs, embracing the Gar- 

 den of the Gods and Monument Park, so curious on account of their 

 geological structure, and well worth mapping as typical geological fea- 

 tures, which might be readily reached by the student traveling from the 

 east. Joining the main party here, we crossed the South Park to the 

 Arkansas Valley, carrying on a running survey of the road as we traveled. 

 By short inarches for five days up the valley, we were enabled to study 

 out, with a good degree of care, the heavy masses of morainal deposits, 

 which, for twenty miles or more, sweep out from the base of the high 

 mountains which border the valley on the west to the present channel 

 of the river. It will, of course, be impossible, in the time devoted to 

 these moraines, to make a carefully-detailed map of them, but enough 

 notes were taken to give quite accurately their relations to each 

 other, their general forms and magnitudes, and their particular trends, 

 together with their relations to the surrounding mountains. 



Leaving this region about the middle of August, we crossed the main 

 divide by way of the Lake Creek Pass and entered the Elk Mountains. 



