438 JULIEN 



tions," along the eastern border of North America from Canada 

 to Georgia, Williams has distinguished two parallel belts along 

 the coast. In his accompanying map he has marked the Bos- 

 ton basin as the known location of one such volcanic center in 

 the more eastern belt ; he also included, as another probable 

 location, the region near Peekskill, nothwithstanding the ab- 

 sence there of any recognized effusive or volcanic eruptives. 

 This was based on the following view : "In New York State 

 there are, as far as the writer is aware, no remains of igneous 

 rock which have solidified at the surface. Nevertheless the 

 isolated and highly differentiated Cortlandt series, near Peeks- 

 kill, presents us with the deeply eroded roots of an ancient vol- 

 cano, probably of Cambrian or Silurian age, whose superficial 

 parts have entirely disappeared. The elaeolite-syenite area in 

 northern New Jersey is probably of the same character." ^ 



Though on the same map no such designation has been made 

 of the sites of New York, Philadelphia and Baltimore, the cor- 

 relation which I think has been demonstrated, by data already 

 given, would connect also the igneous rocks of these tracts, 

 with their characteristic differentiation — gabbros and diorites, 

 pyroxenites and serpentinoids, granites and pegmatites — rather 

 with those of "the basal portions of volcanoes" than with 

 abyssal types. Each of these three places, as well, offers in the 

 disposal and structure of the igneous masses, the same evi- 

 dences of local concentration of igneous activity, to claim a 

 position on the same ancient volcanic belt. 



In the tract from Maryland to Georgia, also, where the lesser 

 intensity of metamorphism has favored escape from effacement, 

 recent investigations have even proven the presence of volcanic 

 effusives, in the form of metarhyolite, diabase, gabbro and their 

 derivatives. 



Mount Manhattan and its Associated Peaks. — If then we are 

 to look upon the acid and basic intrusions, now found crowding 

 the schists of Manhattan Island, as but the lower portions of 

 vents which reached the surface in the form of fluent lavas, we 

 are dwelling, at this site, not merely upon the igneous injections 



1 G, H. Williams, yc//;-. GeoL, II, 1894, 1-31. 



