FETTKE, MANHATTAN SCHIST OF NEW YORK 257 



mations were not actually continuous. At one place, two dikes of basic 

 eruptive rock were found cutting the gneiss but not the overlying quartz- 

 ite. The eruptive rock had weathered more readily than the gneiss and 

 depressions were formed which were later filled with pebbles and sand by 

 the advancing Cambrian sea.®^ This proved that the gneisses were of 

 pre-Cambrian age, while the quartzite and conglomerate were known to 

 be of Cambrian age from fossils found elsewhere in the neighboring re- 

 gions. The apparent conformity evidently was only a structural one due 

 to the general lamination forced upon the rock by the folding. 



In the case of the Fordham gneiss, however, parts of which at least are 

 of sedimentary origin, as shown by the occurrences of interbedded lime- 

 stone in it, the foliation appears to be parallel to the bedding planes, as 

 the bands of interbedded limestone are always parallel to the foliation of 

 the gneiss. 



The fact that the phyllite and schist occur so close together in the 

 vicinity of Peekskill, which has been cited as strong evidence in favor of 

 the later origin of the former, is not as strong an argument as one might 

 at first think when we consider that this change does take place within 

 a not very much greater distance north of the Highlands and also that the 

 intrusion of the Cortland series must have had considerable effect in 

 obliterating transition phases if they did occur. As has already been 

 mentioned, there are still evidences present of what appear to be such 

 transition phases. 



From the above discussion, it is seen that there is still doubt as to the 

 true age of the Manhattan schist. A much more detailed study of the 

 geology of southeastern New York State and western Connecticut and 

 Massachusetts than has yet been attempted will have to be made before a 

 definite conclusion can be arrived at. 



Acknowledgments. The writer is greatly iL^bted to Professor James 

 F. Kemp, at whose suggestion this study of the Manhattan schist was 

 undertaken, and to Professor Charles P. Berkey for many helpful sug- 

 gestions as the work progressed. The work was carried on in the labora- 

 tories of the Department of Geology of Columbia University. 



«iU. S. Geol. Surv. Mon. XXIII, p. 11. 1894. 



