692 R. W. RICHARDS AND G. R. MANSFIELD 
a 
Local unconformity.—Locally the upper cliff-making limestone 
(1) is absent from the section and the Phosphoria formation then 
rests directly upon the more siliceous portion of the Wells formation, 
which in these places is composed of a breccia of chert and quartz- 
ite, similar to that described by Blackwelder (1d) under practically 
identical conditions, and it appears to the authors that this relation- — 
ship represents another instance of a brief erosion interval in this 
part of the geologic section. Dr. Girty says (personal letter) : 
The upper part of the Wells formation is usually nearly barren of fossils. 
Occasionally large Producti of the semi-reticulatus group are found as at Station 
49g (T. 9 S., R. 45 E., sec. 35 SW ¢ SE $); rarely, however, in identifiable 
condition. Some well preserved examples obtained at this horizon near Swan 
Lake (Bannock County) show a form closely allied to Productus Ivesi. In that 
region also a small spiriferoid is very abundant, occurring as silicified fragments 
which project from weathered surfaces like small arched scales. When they 
can be identified these fossils belong to a species of Squamularia related to 
S. perplexa. 
The middle portion (2) comprises 1,700 to 1,800 feet of sandy 
limestone with occasional thin beds of quartzite and sandstones, 
weathering white, red, or yellow, and forming smooth slopes with 
few projecting ledges. This portion is sparingly fossiliferous or 
non-fossiliferous. No fossils have yet been found in it. Locally 
a siliceous facies becomes strongly developed and this portion is 
then comparable with the Weber quartzite of Utah. | 
In the section under discussion sandy and cherty limestones 
with thin interbedded sandstones are conspicuous in the lower 
portion (3) of the Wells formation. The maximum observed 
interval of beds included in this facies is about 750 feet. Within a 
distance of 2 miles to the north the same interval was found on 
careful study to comprise only about too feet of beds. The cherty 
limestones are topographically important as ledge-makers and 
carry a fauna which, according to Dr. Girty, is probably similar 
in age to, although not specifically identical with, that found in 
the Morgan formation of Utah. Blackwelder (1e) has described the 
Morgan formation as composed of red sandstone, shale, and thin 
intercalated limestones, so that, lithologically, it is wholly distinct 
from the cherty limestones described above. Dr. Girty has con- 
