F. GEOGEAPHY. 269 



of the 40th parallel. It consists of a system of vertical and 

 horizontal sketches, based on a rather elaborate triangulation, 

 and checked by numerous angles both vertical and horizontal. 

 This system is peculiarly adapted to a rolling or mountainous 

 country, and in such a country can not be equaled by either 

 of the other modes. It works well, too, in districts of differ- 

 ent character, and is probably, on the whole, the best system 

 on which to base work in the average country of the West. 

 It should, however, be supplemented by good meanders of all 

 the main roads and rivers. In the work of the survey this 

 summer the three systems were employed, and the above re- 

 marks are the immediate result of the summer's observations. 



The party completed about six thousand square miles in 

 the West, being obliged after the trouble with the Indians to 

 leave unworked a small corner in the northwest, which will 

 require about five days to complete. This patch joins di- 

 rectly on to Mr. Gannett's uncompleted area, and lies entire- 

 ly west of the Colorado line. In going to and from the 

 work, six full weeks were spent in marching. Mr. Chitten- 

 den worked about six thousand five hundred square miles, 

 and made eighty-four main stations. 



The geological examination by Mr. Holmes was fruitful 

 of most important results. His investigations were extend- 

 ed from Colorado into portions of Utah, Arizona, and New 

 Mexico. 



No previous study of this region had been made, except- 

 ing that by Dr. Newberry in 1859, of which nothing has 

 been published up to this time. 



In 1874 Dr. Endlich examined the district lying to the 

 east, so that Mr. Holmes took up the work where he left off 

 at 108 W. long., and carried it without difficulty to 109 30'. 

 In general the geology is not greatly complicated. The sec- 

 tion of stratified rocks exposed extends from the lignitic se- 

 ries to the carboniferous, including about two thousand feet 

 of the former, and slight exposures merely of the latter. 

 About eight thousand feet of strata, therefore, passed under 

 examination. Of other rocks, there are four small areas of 

 trachyte, one limited area of metamorphic rock, and a few 

 unimportant dikes. 



Beginning at the east, Dr. Endlich's section on meridian 

 108 includes the entire series, beginning with the lower 



