IOWA ACADEMY OF SCIENCES. 
169 
of its margins while the process of general base leveling was 
going on. 
In the San Andreas range there is found a simple mono- 
clinal block. The profound faulting is on the eastern flank 
of the range. From the foot extends another broad bolson 
plain extending to the foot of the lofty Sierra Blanca. 
The faults represented indicate displacements of 3,000 to 
5,000 feet. 
NORTHWARD EXTENSION OF THE LAKE VALLEY 
LIMESTONE. 
BY CHARLES R. KEYES. 
As a terranal name Lake Valley is applied to a remarka- 
ble blue limestone occurring at the famous silver mining 
camp of the same title, situated in Sierra county. New 
Mexico. The formation is noteworthy for the reason that 
it carries the typical Lower Burlington fauna of Iowa. On 
this account it is of special interest to Iowa geologists. 
The first recognition of the Lower Burlington fauna, a 
thousand miles away from the original locality, is due to 
Mr. Frank Springer, a former Iowan, and the leading 
authority on American crinoids.* 
At Lake Valley the limestone bearing that name is, as at 
Burlington, crinoidal in character. Mr. Springer, in the 
article cited, furnished a considerable list of crinoids as 
well as of other fossils, all of which are the most charac- 
teristic forms of the Lower Burlington limestone of south- 
eastern Iowa. Since the appearance of the paper men- 
tioned, twenty years ago, no further reference has ever 
been made to the Burlington fauna in southwestern United 
States. 
*Am. Jour. Sci. (3), Vol. XXVII, pp. 97-103, 188-J. 
