98 CEMENT MATERIALS AND INDUSTRY. [bull, £ 
PITKIN OR ARCHIMEDES LIMESTONE. 
DESCRIPTION. 
The Pitkin or Archimedes limestone is impure, generally loose te 
tured, and very fossiliferous, varying from bluish gray to brown 
color. In most places it is distinguished by its characteristic fossil, 
spiral-shaped bryozoan of the genus Archimedes, from which i 
former name was derived. The compactness of the stone appears 
vary with the size of the fossils. When they are large the texture 
open, being often but a loosely aggregated mass; when the fossil fraj 
ments are small they are closely compacted and the rock is firm ai 
durable. In some places the formation graduates into sandstone, t| 
change being so gradual that there is no line of demarcation between til 
two. In other places it is very argillaceous, and in most places eontai; 
iron and bituminous matter. In some places it has a loose, shaly stru ■{ 
ture, while in others it occurs in strata 10 feet or more in thickness 
THICKNESS. 
The Pitkin or Archimedes limestone varies in thickness from a fe'i 
inches to 80 feet or more. Its thickness is from 25 to 40 feet in Wasn 
ington County, 80 feet on Pinnacle Mountain, Newton County, all 
apparently more than this on the face of the Boston Mountains, sou 
of Buffalo River, where no measurement was made. Mr. C. E. Si-j 
benthal reports a thickness of 200 feet in the Boston Mountains, so j] 
of Mountain View. 
DISTRIBUTION. 
This limestone is widely distributed over northern Arkansas, oci 
ring at nearly all clear rock exposures at the proper horizon, but as 
is in some places less durable than the overlying rocks, it is frequent 
concealed by talus. In some places it is more durable than the ov 
lying rocks and forms a prominent escarpment along the face of 
mountains. It outcrops along the north face of the Boston Mountai i 
and in many of the northern outliers from Independence County w 
into Indian Territory. It outcrops also on the south side of the 
ton Mountains in several places in Crawford, Franklin, Johnson, 
Newton counties. In Limestone Valley, Franklin County, it hi 
thickness of 100 feet or more. 
It is prominently developed in the group of mountain peaks in 
southern part of Boone County and the northern part of Nei 
County. At Fodder Stack it forms the cap rock, about 100 sqi§ 
feet. On Pinnacle Mountain it occurs in a prominent ledge 80 
thick, 400 feet below the top of the mountain. On Pilot Mount 
at the north end of Boat Mountain, it is 30 feet thick and lies 200 
below the top of the mountain. It is concealed by talus in m* 
places on both Pilot and Boat mountains. 
There are large exposures of the Archimedes limestone on b< 
sides of Buffalo River, in Newton County, on the mountain betw( 
