THE GEOLOGICAL HISTORY OF NEW YORK STATE 49 
cluding the great Taconic mountains) was dry land toward the 
close of the Ordovicic period, while the physical geography of 
western New York for that time is not certainly known. 
It should be noted in passing that the rocks of the Highlands-of- 
the-Hudson were, for a second time, clearly involved in mountain- 
making disturbances. The structural features of the Taconic moun- 
tains are finely exhibited in southeastern New York from Pough- 
keepsie to New York City, where one literally passes across the 
roots of the former great range. The distinct northeast-southwest 
trend of the topographic relief in this part of the State is due to the 
fact that the relief is still largely controlled by the Taconic folds 
and faults. The Hudson river has cut a deep channel across these 
structure lines, and along its banks excellent opportunity is afforded 
for the study of the rocks, folds, faults etc. 
Another feature which must not be overlooked is the profound 
metamorphism of the strata along the main axis of the range. The 
very intense compression, under very high moist heat, caused the 
deeply buried strata along the main axis of uplift to become rather 
plastic, and hence the sediments became more or less foliated and 
crystallized into the various metamorphic rock types, the limestone 
becoming marble, the shale becoming slate or schist, and the sand- 
stone becoming quartzite. Thus we have extensive marble quarries 
in southern Vermont, the slate in.the quarries of Washington 
county, New York, and the Berkshire schist in the Berkshire hills 
of Massachusetts. In passing down the Hudson river from King- 
ston to New York City, the several stages in the metamorphism of 
the Ordovicic slate formation are finely illustrated. Thus, from 
Kingston to near Poughkeepsie the strata are distinctly folded but 
not metamorphosed; from Poughkeepsie tq the Highlands, the 
strata are highly folded and partially metamorphosed, the shale lay- 
ers nearly always having been changed to slate, while the associated 
and more resistant sandstone layers have escaped change; from 
the Highlands to New York City the rocks have been highly folded 
and metamorphosed, both shale and sandstone having been con- 
verted into schist locally called the Manhattan schist. For example, 
the rocks exposed in Central Park are Manhattan schists which are 
believed to have been originally Hudson River shales and sandstones 
which have become thoroughly crystallized by intense meta- 
morphism.’ 
* Professor Berkey has recently suggested the possibility that the Man- 
hattan schist may be Precambric in age; if so, the latter part of this state- 
ment does not apply. 
