eckel.] INDIAN TERRITORY. 145 
CAMBRIAN, ORDOVICIAN, AND SILURIAN LIMESTONES. 
A large part of the Arbuckle Mountains in Indian Territory and of 
the northern foothills of the Wichita Mountains in southern Oklahoma 
are composed of a great section of Cambrian, Ordovician, and Silurian 
limestones," having a total thickness of nearly 8,000 feet. There are 
three distinct limestone formations in this section, separated by 
deposits chiefly of shale. 
ARBUCKLE LIMESTONE. 
The lowest of these, known as the Arbuckle limestone, consists of 
limestone and dolomite of Cambro-Ordovician age 4,000 to 6,000 feet 
thick. Samples from the lower part and from the top downward 600 
or TOO feet were tested for magnesia and lime and showed a very small 
percentage of magnesia. Beds 2,500 feet below the top contain a small 
amount of magnesia. Probably 2,000 feet of massive beds in the cen- 
tral part of the formation are dolomitic. A sample from approxi- 
mately the middle of the formation yielded 29.4 per cent of lime and 
19.2 per cent of magnesia, showing it to be a nearl} 7 normal dolomite. 
A sample from the lower part of this dolomitic zone showed contents 
of 33.1 per cent of lime and 14.3 per cent of magnesia. The Arbuckle 
limestone outcrops over more than three-fourths of the surface of the 
central part of the Arbuckle Mountain district, inclosing pre-Cambrian 
granite and granite-porphyry. Almost all of the limestones of the 
Wichita Mountains belong to this formation, which is line-textured 
and generally hard. 
VIOLA FORM ATI OS. 
An Ordovician limestone, 500 to 700 feet thick, known as the Viola 
ormation, outcrops in a belt in the border of the Arbuckle Mountains 
and in small areas in the central part. It makes three small hills near 
ainy Mountain Mission, in the Wichita Mountains. This formation 
s of limestone, with the exception of local deposits of chert. Chem- 
ical tests of samples from this limestone in the Arbuckle Mountains 
how it to contain very little magnesia. It is tine-textured and gen- 
erally hard. 
SYLVAN SUA I.E. 
Above the Viola limestones is a deposit of greenish clay 50 to 300 
feet in thickness, known as the Sylvan shale. This clay outcrops in 
narrow belts and has a wide distribution in the Arbuckle Mountains, 
but in the Wichita Mountains both it and the Hunton are concealed 
by Permian deposits. 
a These limestones are described in detail in the Atoka and Tishomingo folios Nos. 79 and 98. Also 
p the Geology of the Arbuckle and Wichita Mountains: Prof. Paper U. S. Geol. Survey, No. 31. 
Bull. 243—05 10 
