466 ELEMENTARY GEOLOGY 
tain growth in the east; for although they were 
deposited horizontally in the sea, or in bays, they are 
now tilted, and in some places considerably broken. 
Among them are found volcanic rocks, — black trap, or 
diabase. This class of lava is found in the Triassic 
strata from Nova Scotia to Pennsylvania, and even 
south of this. Throughout this entire area, the trap 
is of the same nature. It represents the last period 
of volcanic eruption in the history of the eastern 
part of this country. 
The lava flows from this system of volcanoes, now forming 
the prominent hills of Cape Blomidon, Nova Scotia, the Hanging 
Hills of Meriden, Conn., Mounts Tom and Holyoke, in Massa- 
chusetts, the East and West Rocks of New Haven, Conn., the 
Palisades of the Hudson, and the hills near Paterson and 
Orange, N. J. 
In the Far West, the close of the Juratrias was 
marked by an extensive mountain growth, similar to 
that of the Appalachians. During this time the Sierra 
Nevada were elevated to a great height. Among the 
strata of these mountains are found highly altered 
slates of Juratrias age. These were therefore de- 
posited at that time, and have since been raised, 
folded, and changed from clay sediment to hard slate 
rocks. Previous to this time the history of the Sierra 
had been complex, and their later development’ is 
also complicated. 
