Scientific Intelligence. 235 
are given in five chapters Pipebea aati cae to the five maps of the 
Atlas illustrating the regi 
The first chapter treats "of the Colorado range, its mountains, 
plains and rocks, the Laramie Plains, Medicine Bow Range, the 
North Park and Park Range, the Bridger’ Pass Region, the 
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ocks, 
The pent Hills described by Mr. Hague in the first chapter, 
include the part of the eastern Clore range mostly within the 
limits of the 41st and 42d parallels. The altitude of the peaks is 
generally between 7,800 and 8,300 feet, one of the apa reaching 
probably a height of 9,000 feet, This part of the range is an anti- 
clinal, having an axis of granite and granitoid rocks of Archzan 
age, on either side of which lie unconformably sandstones and 
“reddish ara - rocks compo u and feldspar,” 
becoming to rth and south decidedly schistose, being well- 
and in another 1°40 per cent, showing, as Mr. Hague remarks, that 
the triclinic feldspar cag be either albite or oligoclase. The 
mica is biotite, but with some lepidomelane. Tron Mountain is a 
labradorite granitoid rock, with cleavable labradorite, described 
by Professor Zirkel, in his Survey Report, as gabbro. The amount 
of foliated pyroxene is small. On oigg west side of the Hills, 
gra wes occurs in thin beds and sea 
e geological features onaneeacuii the Laramie omen con- 
tinues southward along the Colorado Range. The granite of the 
summit of Gray’s Peak afforded on analysis the same saa pontiios 
essentially as that of ne Hills. The ov ei fowd peaeepens for- 
mations bordering the mountain range are ted to have a 
800 to 300; the Jurassic, 200; the Cretaceous, 4.3 0 feet gr 
feet of the Dakota group, 1 ,000 of the Colorado seat 1,500 of 
the Fox Hill, and 1,500 of the Laramie). The Paleozvie beds con- 
tinue along the eastern foot hills for nearly 70 miles, ret then 
disappear, none bei ing found north of Colorado Sprin 
Triassic beds consist of red sandstone with some red me and 
thin beds of limestone, and, in some localities, i ieeed lar eposite 
OF slightly red two to twent five feet poatge! The fare rassic 
ahent ish in ti fist h ora 
