116 History of the Geology of New York Island. 



Hornblende, Anthophyllite, and other masses. — Similar 

 remarks to the above on granite will apply to these masses; 

 they are simply different conditions of the same elementary 

 materials as the gneiss, merely different forms of metamor- 

 phism. 



Limestone.' — The Kingsbridge mass has been fully described 

 and needs no farther remarks from me, except that, on the 

 western bou: ds, there is evidently a partial overthrow of the 

 mass, so that the western wall has an eastern dip, similar to the 

 eastern, while the central is vertical. 



East of 6th avenue, in grading W. 132d st., another bed of 

 limestone is revealed, having an eastern and western dip on its 

 respective flanks; its arch is plainly visible, and the gneiss 

 repo-ing conformably upon it. This is a continuation south- 

 wards of the limestone of the Clove, north of McComb's Dam, 

 Westchester Co. 



IEAST 122?? STREET N.Y 

 B* 



Section of Limestone and Gneiss. 



Between 4th and 3d avenues, E. 123d st. cuts through 

 another bed of limestone, showing a double fold, with gneiss • 

 on the east flank, and reposing in the fold. ' In E. 122d st. the 

 same bed has been cut through, revealing the broken arch of 

 the fold, with gneiss on the western flank, and broken gneiss 

 on the eastern. The middle of the arch is also to be seen, dip- 

 ping gently westwards and abruptly eastwards. Again it was 

 seen in the excavation for a culvert in E. 50th st., between 3d 

 and 4th avenues. The gneiss of the arch was much brokeD, 

 the axis of limestone revealed at the depth of about eighteen 

 feet beneath the street. The angle of the dip about equal on 

 either side. The arch of this fold can be seen in the gneiss E. 

 49th st., in front of the " Protestant Episcopal Orphans' Home." 



