456 ELEMENTARY GEOLOGY 
that during the Niagara at least a part of New England was 
beneath the sea. It is possible that at previous times this had 
also been true, but later changes have so altered the rocks of 
these states, that their history is difficult to decipher. The con- 
dition of New England at this time appears to have been that of 
mountains of considerable height, penetrated by arms of the sea. 
One of these arms was the Connecticut valley, which again and 
again during the development of the country, has been alternately 
raised above the level of the sea and depressed beneath it. 
After the Niagara epoch there occurred a slow change back 
toward shallow-water conditions, which permitted the deposit of 
shales upon the limestone of the Niagara. While these rocks 
(the Onondaga) were being accumulated, the conditions in central 
New York changed absolutely, so that for a time it was possible 
for beds of rock-salt and gypsum to be deposited. For some 
reason, which cannot be stated with definiteness at present, large 
areas of shallow salt water were subjected to evaporation, so that 
between the beds of shale, layers of gypsum and salt were gath- 
ered. These salt-bearing beds constitute the Salina division of 
the Onondaga. 
It is possible that the accumulation of this salt proves that 
during the time of its deposit, the climate of central New York 
was arid, like that of parts of the west at present, and that the 
region was occupied by an arm of the sea, temporarily separated 
from the open ocean, as the Caspian is to-day, and as at any time, 
by shght geological changes, the Mediterranean may come to be. 
It cannot be said that this is proved, for it is also possible that 
this part of the state was a great shallow arm of the sea, subjected 
to evaporation, and so cut off from its supply of pure salt water 
that salt was precipitated as it is in salt vats. All of these beds 
are found to be unusually free of fossils. We would expect this 
to be the case, for in a body of water precipitating salt, life could 
not exist in abundance. The Onondaga group has a thickness 
of from three hundred to fourteen hundred feet, and in this there 
are rock-salt beds whose total thickness in some places is one 
hundred feet. 
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