162 J. V. Lewis— Palisade Diabase of New Jersey. 



The contact metamorphic effects of the sill at Hoboken, New 

 Jersey, have been described by Andreae and Osann,* who show 

 that it is of exomorphic pneumatolytic character. To the four 

 types of hornfels which they describe, J. D. Irving f has added 

 five others, and the present studies, in which no attempt has 

 been made to present a complete series of alteration products, 

 have brought out eight additional types of hornfels and four of 

 metamorphic arkose. These might be extended almost indefi- 

 nitely, since they do not occur as sharply defined types, but 

 present various degrees of gradation from one to another. 

 Furthermore, they do not form zones or belts in any systematic 

 order with relation to the intrusive rock, but alternate irregu- 

 larly throughout all parts of the zone of metamorplrism. It is 

 evident, therefore, that the types observed are not the results 

 of varying degrees of metamorphism, but are dependent only 

 on original variations in the composition of the shales and sand- 

 stones themselves.;}: 



* Andreae and Osann, Tiefen contacte an intrusiven Diabasen von New 

 Jersey ; Verh. d. Naturh. Med. Ver. zu Heidelberg. N. F. V., Bd. I, 1892. 



f School of Mines Quarterly, vol. xx, pp. 213-223, 1899. 



j For descriptions of these rocks, and of other igneous rocks besides the 

 great intrusive sill, see " Petrography of the Newark Igneous Rocks of New 

 Jersey," Ann. Report of the State Geologist of New Jersey for 1907, pp. 

 98-169. 



