J. F. Kemp — Extension of the Cortlandt Series. 253 



rock above referred to, but I was unable to find it myself. If 

 so, it probably furnished the included masses there mentioned. 



Along the roadside in B and C, 5, a mass of included gneiss 

 is to be seen. This is very firmly crystalline, appearing al- 

 most massive in character, and is more compact and hard than 

 the neighboring gneiss in place. • It is said that stone for bridge - 

 piers and culverts was obtained here by the West Shore Rail- 

 way engineers on account of its strength. 



While this area is far smaller than the original Cortlandt, it 

 yet is large enough to exhibit in its mass very perfectly the 

 coarse, noncrystalline structure, characteristic of plutonic 

 masses, shading off toward the contact into finely crystalline or 

 porphyritic types. Moreover, as the general axes of both this 

 area and the main Cortlandt run approximately parallel to the 

 strike of the gneiss and limestone the inference is suggested 

 that they welled forth from longitudinal fissures produced by 

 the general folding. Also that the Rosetown mass broke across 

 and through the intervening beds of limestone and gneiss and 

 formed the westerly extension and that in its passage it took 

 up the masses of limestone and gneiss now found included. 

 From the undisturbed condition and unconformable strike of 

 the neighboring Triassic beds it is safe to infer that the out- 

 break was previous to the Trias. It is clearly subsequent to 

 the Tompkins Cove limestone. If this is Cambrian as seems in- 

 creasingly probable the intrusion of the Cortlandt series cer- 

 tainly occurred in the Palaeozoic* We would infer, however, 

 from its general noncrystalline character that the mass, as now 

 seen, solidified a considerable distance beneath the surface and 

 under great pressure and slow cooling. 



The credit of the discovery of this area belongs to Dr. N". L. 

 Britton, and the writer is indebted to him for the suggestion 

 of its elaboration. It is not improbable that other outlying 

 masses may be found in further field work in the Highlands. 

 In the rear of the Tompkins Cove School numerous stray pieces 

 of feldspar porphyry, like the rock near Montrose Station have 

 been found by the writer quite disconnected with either area. 

 In the foot of the Dunderberg the West Shore R. R. cuts show 

 numerous dikes which seem to be closely related. From this 

 same region Matherf mentions under the name greenstone not 

 a few localities of probably intrusive rock, but his descriptions 

 are too unsystematic to serve as other than suggestions for 

 subsequent workers. 



Geological Laboratory, Cornell University, Ithaca, N. Y. 



* J. D. Dana. This Jour., Ill, vol. xxviii. p. 886. 



flST. Y. State Survey, Geo!.. 1st Dist, p. 539 and elsewhere. 



