226 KANSAS CITY REVIEW OF SCIENCE. 



of 1873 several valuable lode claims were being worked for gold, while carbon, 

 antes of lead and copper, iron pyrites, zinc blende, etc., were found, A vast 

 body of iron ore was also reported by Hayden, "carrying gold enough to pay 

 moderately," also, "excellent galena carrying silver in the quartzites near the iron 

 vein." No indication, apparently, was observed of the vast quantities of silver ore 

 that have within four years brought the district to the position of the richest min- 

 ing camp in the world and caused Leadville to leap from a grubbing town of two 

 or three hundred people to a thriving city of nearly 20,000. At that time two 

 mines, the "Printer Boy" and the "Pilot" were yielding less than $50,000 per 

 annum, now more than thirty mines are being worked, producing $13,170,576 in 

 1881. 



The geology of this region is quite difficult to understand except by the most 

 extensive generalization, as will be seen from the following description by Dr. 

 Hayden: "On the summit between Mosquito, Bird's Eye and Evans Gulches 

 broken masses of the quartzites and trachytes seem to have moved down a con- 

 siderable distance from their places and are deposited in the form of windrows as 

 if there had been glacier movements there. ^ * >i< q^^ q^ 



the peculiar geological features in this range is the trachytic beds, which appear 

 to be interstratified with the older sedimentary rocks. These igneous layers vary 

 much in thickness, and appear and disappear, reach a thickness of 1,000 feet or 

 more, and diminish in a short distance to a few feet or disappear entirely. And 

 yet upon the outcropping of the great uplifted ridges, or in the deep gulches 

 where not unfrequently 2,000 vertical feet of rocks are shown in their order of 

 superposition, these trachytes seem to have flowed out over the surface of the Si- 

 lurian quartzites or, in other words, are interstratified among the old silurian 

 limestones and quartzites as if they might be of the same age and have been ele- 

 vated with them." 



S. F. Emmons, Geologist in charge of the Rocky Mountain Division U. S. 

 Geological Survey, in his " Abstract of a Report upon the Geology and Mining 

 Industry of Leadville, 1881," describes more minutely the peculiar geological 

 features immediately about Leadville, as condensed by the American Journal of 

 Science for July. 



"The Paleozoic rocks of the Mosquito Range have a thickness of 4,050 to 

 5,600 feet and are more or less folded and faulted. They comprise (i) 200 feet 

 of Cambrian or Primordial, chiefly quartzites; (2) over these, 200 of Silurian 

 {whiie or dolomitic limestone and quartzite); and (3) 3700 to 4200 of Carbonifer- 

 ous, which last have 200 feet of limestone, called the blue limestone, at base and 

 1,000 to 1,500 at top (Upper Measures), with grits (Weber grits), sandstones 

 and shales, partly calcareous, between. In the Kanab section on the Colorado, 

 the Paleozoic has about the same thickness (85 feet of it referred to the Permian); 

 but m the Wahsatch section cited, the thickness is 30,000 feet, 12,000 referred to 

 the Cambrian, 3400 to the Silurian and Devonian, 15,000 to the Carboniferous 

 and 650 to the Permian. 



