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



spar crystals 0*l mm to 03 mm , evidently produced from the large 

 quartz and feldspar of the gneiss by contact. In polarized 

 light this resembles a beautiful fine mosaic (kataklasstructur ?) 

 apparently protecting the gneiss from the further metamor- 

 phosing action of the dike. These contact phenomena are to be 

 seen very generally around the area but the best exposure is 

 perhaps in the roadside in D, 5 and C, 6. On the roadside 

 in A, 6 where the area trends to the north at the site of a 

 supposed silver mine is a dike which proves to be a horn- 

 blende porphyrite which is interesting as exhibiting a dif- 

 ferent facies from the other contact dikes, and one more 

 of the character that would on a priori grounds be expected. 

 It seems reasonable to infer that this latter was intruded 

 between walls possessing less heat for some reason than those 

 of the former, and was thus more suddenly chilled. 



From somewhere near this same locality a piece of so-called 

 iron ore was given me by a farmer, but the exact point was 

 kept secret. It appears on section to be a hard and very com- 

 pact mixture of magnetite and emery or corundum and to be 

 thus a similar occurrence to those in the main Cortlandt.* 



In the bed of the brook below the M. E. parsonage (B, 8) is 

 another most peculiar contact mass. The rock is of porphyritic 

 character very similar to the curious porphyritic rocks occurring 

 near Montrose. It contains, however, all manner of included 

 masses of gneiss and limestone, resembling a pudding into 

 which the enclosed masses have been stirred. In macroscopic 

 characters the enclosed limestone resembles very closely the 

 mass on the summit of Stony Pt. Under the microscope it is 

 seen to be an exceedingly finely crystalline aggregate of calcite 

 crystals ^ij mm in diameter mingled with some, more brightly 

 polarizing but undetermined mineral in crystals no larger. 

 Scattered grains of pyrite are also to be seen. 



Back of the lime-kiln in B, 8 and 9 is found the mass of in- 

 cluded marble above referred to. This is colored dead black on 

 the map. As much as thirty feet in thickness have been ex- 

 posed by the quarrying, but the exact contact with the diorites 

 is not shown. They however are found but a short distance 

 north and south, proving it to be an included mass. In general 

 the limestone is a beautiful white crystalline marble, in places 

 very curiously banded. There are, however, numerous masses 

 along its outer edges which are shown by the sections to con- 

 sist quite entirely of tremolite. The limestone also exhibits 

 the half fused appearance of similar contact masses the world 

 over. A similar limestone or marble is said by the farmers to 

 have been found in the bed of the brook near the porphyritic 



* J. D. Dana. This Jour., Ill, xx, p. 199-200.— G-. H. Williams, ibid., xxxiii, 

 p. 194. 



