CLARK: TACONIC REVOLUTION. 159 
Crystalline Rocks of New York City, New Jersey 
Highlands, and Southward. 
Throughout the area designated above, the same general 
conditions prevail as characterize the region of the Taconic 
Mountains: metamorphosed Cambrian and Ordovician rocks 
with no overlying younger Palaeozoic strata. "This similarity of 
(conditions doubtless gave rise to the belief that the region south 
of New England had itself suffered mountain-building in the 
late Ordovician, That there is no evidence for this belief is 
shown by the extracts and remarks below. 
Neic York City. — Dana supposed that the original Taconic 
Mountains extended southward through Westchester County, 
New York, to New York City, and thence on to Virginia. The 
evidence for this around New York City is unsatisfactory. Un- 
fossiliferous crystalline rocks of supposedly Cambrian and Or- 
dovician ages are the only Pala*eozoic representatives. These 
are the Stockbridge dolomite and the Hudson schist. The former 
was correlated with the Stockbridge dolomite of western New 
England by Merrill on the grounds of stratigraphic continuity. 
Of the latter Merrill writes: "The schist of New York district is 
given the name Hudson because it continues northward and con- 
nects stratigraphically with the great areas of slate and shale 
along the Hudson River which have been called respectively the 
Hudson slate and the Hudson shale. The Hudson schist, 
Hudson slate, and Hudson shale represent different phases of 
alteration of the same original rock, and together they form the 
Hudson formation."^ 
Berkey, writing more recently, has been inclined to doubt 
that the Hudson schist is of Palaeozoic age.^ He descriljes it 
under the name of the Manhattan schist, and has sought to show 
that it is more probably of late pre-Cambrian age. Whichever 
view l>e correct, the structur(» of the region cannot be considered 
as proving late Ordovician mountain-building. It is particularly 
~MemU, G. P. U. S. Geol. Siirv., Geol. Atlas, New York City foUo, 
no. 83, p. 4, 1902. 
'Berkey, C. P. Structural and stratifrraphieal fejitures of the basal 
gneisses of the Highlands. Bull. N. Y. State Mus., no. 107. p. 370, et<?., 
1907; also Geology of the New York City (Catskill) Aquediict. Bull. 
N. Y. State Mus., no. 146, p. 47-48, 1911. 
