PALEOZOIC SERIES. 29 



and a few miles to the southward of the forty-first parallel, Eed Beds of 

 the Triassic occur, lying directly upon the metamorphic rocks, and from 

 that point southward, for a long distance, beyond the limit of our map, 

 form the lowest member of the series exposed. According to the observa- 

 tions of Mr. A. E,. Marvine^ and Dr. A. C. Peale, the Palseozoic strata do 

 not re-appear again north of Colorado Springs. The persistency of the 

 lower beds along the foot-hills for nearly 70 miles, and their sudden disap- 

 pearance, not to re-appear again north of latitude 39°, is an interesting 

 feature in the structural peculiarities of the range. 



Paleozoic Series. — By reference to Map I, east half, of the geo- 

 logical sheets in the accompanying atlas, it will be seen that the ridges, 

 which are formed of the Palaeozoic rocks along the east base of the Colorado 

 Range, are represented in but one color; the one employed on the other 

 sheets to designate the Upper Coal-Measure limestone. So far as our obser- 

 vations in these ridges have been made, the rocks of the Coal-Measures are 

 the only formations that have been definitely determined by palseontological 

 evidence, and these occupy the greater part of the entire thickness of sand- 

 stones and limestones represented in the series, extending from the summit 

 downward to within 150 feet of the base. 



According to the published reports of Dr. F. V. Hayden^ and Prof. 

 N. H. Winchell,' and to the verbal communications of Mr. Henry Newton, 

 of the Black Hills expedition of 1875, primordial fossils, representing Oho- 

 lella and Lingulepis, have been collected in the lower coarse sandstones at 

 the base of the series in the Black Hills to the northeast. The detailed sec- 

 tions from the Black Hills agree so closely Math those made from the I^ara- 

 mie Hills that it would seem most probable that the entire series represented 

 in one locality would be found in the other; and that the 100 to 150 feet 

 of reddish sandstones at the base of the series in the Laramie Hills may yet 

 yield the lower forms of life, as found farther to the north. 



For this reason, the entire series of conformable rocks below the Triassic 



has been considered as compressed within the few hundred feet of Palaeozoic 



^United States Geological and Geographical Survey of Colorado, 1873. 

 * Geological Report of the Exploration of the Yellowstone and Missouri Rivers, 

 P. V. Hayden, 1859-60. 



^Reconnaissance of the Black Hills of Dakota, 1874, N. H. Wiuchell. 



