258 
EEPORT OF THE AMERICAN COMMITTEE. 
upon the subject, and the papers published amount to more than 
twice that number. The difficulties of the subject are caused by 
the easy disintegration of the rock and consequent covering of it 
with earth almost everywhere — by the unusual uniformity of the 
rock in color and composition, which renders difficult the tracing 
of faults or other disturbances, and by the scarcity of marine 
o 
M 
OQ 
m 
< 
European 
(Dana.) 
New- 
Jersey. 
Virginia. 
North 
Carolina. 
Rocky 
Mt. 
Region. 
Lower Lias 
Keuper 
Jurassic? 
Arkose 
(Archean) 
Jurassic ? 
Coal 
Bearing 
(Archean) 
Upper Red 
Sandstone 
Coal 
Bearing 
Muschel- 
kalk 
Lower "Red 
Sandstone 
(Archean) 
Bunter- 
Sandstein 
(Permian) 
invertebrate fossils. The relative time and mode of occurrence 
of the eruptive rocks are also among the subjects of discussion, 
and information is still needed upon all these points before satis- 
factory conclusions can be drawn. 
In the series no Jurassic rocks can be clearly separated from 
the Triassic, and no line defining the upper limit of the latter 
has yet been drawn. 
The Trias and Jurassic are extensively represented west of 
the Mississippi. There is a general resemblance of these to the 
