CARBONIFEROUS FORMATIONS. Bs) 
This accounts for the fineness of the mud and the widespread presence of 
magnesia. The first indication that the sedimentary beds had been worn 
away and the granite exposed on the land is the occurrence of mica scales 
and other detrital materials in the gray limestone which overlies the black 
carbonaceous limestones, and which has been taken as the base of the 
Maroon. The amount of granitic material rapidly increases from this point 
upward, till within a hundred feet or so it forms the chief and finally almost 
the only constituent in the sediments. 
Thickness of the Weber formation —The great Silver fault, which runs through 
most of the district, at a slight angle to the bedding, has the Weber lime- 
stone generally on its west side. Part of the formation has therefore been 
eut out by the faulting, but how much it is not always easy to ascertain, 
The most favorable places for measuring the thickness of the formation are 
at the southern end of the area of the Tourtelotte Park special sheet, on the 
west side of the Castle Creek fault, and from the northern end of the area 
of the Hunter Park sheet through that of the Lenado special sheet. In the 
former of these places the thickness is made somewhat uncertain by the 
existence of an unknown number of small faults consequent upon the Castle 
Creek fault, and forming only a small angle with the bedding planes. In 
the latter place the presence of the Silver fault renders the measurement 
dubious. So far as can be judged from the character of the rocks, however, 
we have in both these places a tolerably complete section, and measure- 
ments show that the maximum thickness can not be much less than 1,000 
feet. 
MAROON FORMATION. 
Above the Weber formation comes a great thickness of mixed are- 
naceous and calcareous sediments, forming impure grits and thin-bedded 
shaly limestones. This formation is calcareous and thin bedded at first, 
but becomes more massive and arenaceous farther up. The general color 
is a peculiar dark red, which has been characterized by different geologists 
in various parts of the region as chocolate red, venetian red, purplish red, 
and maroon. The formation as existing im various parts of the Rocky 
Mountain region has been described by the geologists of the Hayden 
Survey;' as found in the Mosquito district it has been described by Mr. 
1Ann. Rept. U.S. Geol. and Geog. Surv. Terr., 1873, pp. 18, 105; 18/4, p. 114. 
MON XXXI 3 
