AUTHORS’ ABSTRACTS pyle 
porphyry; basalt occurs as a surface flow, and andesitic débris in the 
tuffs and conglomerates of the bedded series. 
Among sedimentary rocks in this region are found representatives 
of the principal formations from the Archean up to the close of the 
Mesozoic, with some later formations whose exact age is still somewhat 
doubtful. 
The Cambrian is represented by the Sawatch quartzite, which con- 
sists of 50 to 200 feet of white quartzite, conglomeritic at the base, and 
at certain horizons persistently glauconitic; its fossils are of the Pots- 
dam type. 
The Silurian beds, which are locally called the Yule limestone, in 
an aggregate thickness of 350 to 450 feet consist mainly of limestones, 
with quartzite at the base and more shaly beds at the top. They con- 
tain the same fish remains that characterize the Harding sandstone of 
the Canyon City section, but organic remains have not been discovered 
in sufficient abundance to admit of the subdivison of the series on a 
paleontological basis. 
The Carboniferous is represented by three subdivisions. (1) The 
Leadville limestone, or Lower Carboniferous, has a thickness of 400- 
525 feet of dark-gray or blue limestones, with some intercalated quartz- 
ites and shales. Above this is (2) the Weber formation, which consists 
of 100-500 feet of shales and limestones, carrying fossils of Coal 
Measure type. The upper member, known as (3) the Morgan con- 
glomerate, consists mainly, as its name indicates, of conglomerates, 
which are characterized by the local abundance of pebbles of limestone. 
It has an observed maximum thickness of 4500 feet, and in its upper 
portion resembles lithologically the Red Beds, generally assigned to 
the Trias. 
The Juratrias, whose beds are separated from the last mentioned by 
a great unconformity, is represented by the Gunnison formation, which 
consists of a heavy white sandstone about roo feet in thickness, over- 
lain by shales and a little limestone, and carries a fresh-water fauna of 
supposed Jurassic age. 
The Cretaceous is represented by five recognized subdivisions: 
The Dakota quartzite, 50-300 feet thick; the Benton shale, 150-300 
feet thick; the Niobrara limestone, 100-200 feet thick; the Montana 
formation, comprising the Pierre shales and Fox Hills sandstones, 
600-2000 feet thick; the prevailing lithologic characteristics of each 
of which is indicated by its name. Among later beds are the Ohio 
