194 GEOLOGICAL SUEVEY OF THE TEREITOKIES. 



C H A P T E E I . 



FEOM DENVEE TO COLOEADO SPEINGS — FEONT EANGE— BEEGEN 

 PAEK — HAYDEN PAEK. 



On tlie 29tli of May the division of the expedition with which I was 

 connected as geologist left Denver, and proceeded southward to com- 

 mence the summer's w^ork. On the 1st of June we crossed the northern 

 line of our district a short distance north of the mouth of the canon of 

 the South Platte Eiver. Here our work commenced. As we look from 

 the plains westward before us rises a plateau-like mass of hills, beyond 

 which we discern the snowy peaks of the main range. I will consider, 

 first, the front range, or the foot-hills, as they are called by the settlers. 

 Seen from a distp^nce, the height of this range seems very uniform. As- 

 cending the hills, however, we find they are much cut up by the various 

 small streams that drain them. The larige is made up almost entirely 

 of plutonic rocks, so covered up that little can be definitely determined 

 in regard to them. ISlorth of the Pltttte caiion they w^ere thoroughly 

 studied by Mr. Marvine, and to his report I refer the reader. On the 

 south the general strike seems to be nearly north and south. The incli- 

 nation at some points seems to be toward the west, and at others to the 

 east. There is probably a series of folds, for the elucidation of which 

 more time than "we were able to give will be required. Toward the out- 

 side of the range the schists are of a bright-red color, from the predom- 

 inance of the crystals of flesh-colored feldspar. They are also porphyr- 

 itic. As we approach the center of the plateau, gray schists prevail, 

 much finer grained, and containing considerable epidote : they are also 

 more micaceous. The general elevation of the range, two miles south of 

 the Platte Eiver, is 6,735* feet. Five miles farther, at Station ]^o. 7, it 

 is 7,979 feet. About nine miles south of this station we have, on the 

 western side of the range, rising considerably above it, a rough granite 

 ridge, to which the name Platte Mountain has been given. Its elevation 

 above sea-level is 9,027 feet. About five miles below it the general ele- 

 vation is 8,448 feet, while on the eastern edge of the range, twelve miles 

 south of Platte Mountain, the elevation at Station I^o. 11 is 8,986 feet, 

 and this, five miles farther south, at Station ^N^o. 12, increases to 9,124 

 feet. We see, therefore, that as we go south there is a gradual rise 

 toward Pike's Peak, which seems to be the culminating point. The 

 width of the range varies somewhat, but it will average from six to eight 

 miles. The question of the elevation of the range, as well as the con- 

 sideration of its western slope, I will leave to a subsequent portion of the 

 chapter. I will refer next to the sedimentary formations, which are 

 beautifully exposed along the eastern edge of the range, extending from 

 our northern to our southern line, south of Pike's Peak. My first sec- 

 tion was made on the south side of the South Platte Eiver, just as it 

 leaves the canon, and flows toward the plains. Its course here is about 

 north 70° east. 



Eesting immediately upon the granite rocks we have very coarse 

 sandstones, mottled red and white. Close to the granite the sandstone 

 is coarsest, and contains pieces of unchanged granite. In other places 

 the sandstone appears to pass by gradation into the granite. They were 



* All the elevations in this report are based on the elevation of Denver, which is 

 assumed at 5,069 feet above sea-level. 



