16 NEW YORK STATE MUSEUM 



ridge succeeds ridge, each of which runs out and diminishes in 

 height until it disappears below the rocks which are generally con- 

 sidered of more recent origin" (p. 517)- 



Since Mather's time no very large amount of areal work on the 

 Highlands has been published, although various investigators have 

 worked in the region in connection with special problems. 



James D. Dana in 1880 studied the limestones of Westchester 

 county,^ He states that the limestones are interbedded with the 

 gneisses and that Westchester county owes many of its topographic 

 features to its limestone belts which determine river valleys, marshes 

 and lakes (p. 28). 



In the West Point quadrangle he observed that the limestones in 

 the southern part have an east-west trend which is abnormal in this 

 region, and also that the two largest valleys in the Highlands proper, 

 Conopus hollow and Peekskill hollow, are developed on limestone. 



In 1896 The University of the State of New York published a 

 map of the State which represents the Hihgland region differently 

 from the map published with this bulletin. The chief discrepancy 

 lies in their correlation of all the limestones as upper Silurian. The 

 more recent work in the area indicates the presence of both Precam- 

 brian and Paleozoic limestones. 



On the adjoining regions of New York, Pennsylvania, Massachu- 

 setts and Connecticut, various papers ^ have been published. 



In the Raritan folio® a more fully matured and complete descrip- 

 tions of the formational units recognized by the New Jersey Survey 

 may be found. The same divisions are supported as in the earlier 

 publication and thus the names Pochuck, Losee and Byram gneiss 

 have become firmly established. 



The authors of these New Jersey folios divide the Precambrian 

 series into two main types, sedimentary and igneous. The sedi- 

 mentary is now represented only by the limestone strata and by part 



*Dana, J. D., Limestone Belts of Westchester County, New York Amer. 

 Jour. Sci. and Art. v. 20. 1880. 



* Geological Map of the State of New York. F. J. H. Merrill. 



'^U. S. Geol. Survey Geologic Folio No. i6i. Franklin Furnace Folio 

 (1908). Spencer, A. C, Kummel, H. B., Wolff, J. K, Salisbury, R. D., 

 Palache, Charles. 



U. S. Geol. Survey Geologic Folio No. 162. The Philadelphia Folio. 

 Bascom, F., Clark, H. B., Darton, N. H., Kummel, H. B., Salisbury, R. D., 

 Miller, B. L., Knapp, C. N. 



Geological Map of Connecticut. Conn. Geol. and Nat. Hist. Sur. Bui. 7 

 (1906). Gregory, H. E., and Robinson, H. H. 



Geological Map of Massachusetts and Rhode Island, U. S. Geol. Survey 

 Bui. 597 (1916). Emerson, B. K. 



* Geologic Folio No. 191, U. S. Geol. Survey (1914). The Raritan Quad- 

 rangle. W. S. Bayley, R. D. Salisbury and H. B. Kummel. 



