264 F. Prime, Jr.—Lower Silurian Fossils. 
grains of pyrite disseminated through it, which weather out on 
exposure, leaving minute cavities behind. Numerous analyses 
have shown the presence of ferrous carbonate varying in amount 
from 0°588 to 1°305 per cent. 
A peculiarity of the limestone is that it is often brecciated, 
the fragments being composed exclusively of limestone, cemented 
together by calcite or dolomite. The brecciated appearance is 
rarely visible on fresh fracture, being usually brought to view 
y weathering. When seen in place it will usually be found 
that one or more brecciated beds occur between two others 
which do not exhibit this peculiarity. As the beds of the No. 
II limestone have been much disturbed by the force which ele- 
vated the South Mountain range, the probable explanation of 
this brecciation is that a very hard, unyielding bed occurs be- 
tween two more pliable ones; that these, when subjected to the 
lateral thrust of the uprising mass of the South Mountains, 
have couformed themselves to the folds of the strata, while the 
harder one, being unable to do this, has been fractured and re- 
cemented in sitt by the percolation of calcareous waters. 
stone (according to these observers) having been formed from 
the lower, the brecciated limestones are adduced as evidences 
of upheaval and shore action. 
The explanation I have offered of the formation of the bree- 
ciated limestone is both more in accordance with the facts ob- 
served and with the generall accepted view of the deep-sea 
formation of limestone than the hypothesis above stated ; for 
the brecciated limestones are as common near the base of the 
series as at the top. 
ides, the genus Monocraterion found in the Lehi 
limestone belongs to the same family as Scolithus, saat is there- 
fore no greater proof of age than the latter; and it occurs in 
o. II, being not more 
than fifty to one hundred feet from the overlying Calciferous 
and Trenton. 
_humber a dozen specimens, and have been found in but four 
localities. At Helfrich’s Spring, about two and a half miles 
west end of the hill, near 
of the creek forming the s 
species of Monocraterion, as yet undescribed. Of this half a 
