PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 217 



Aporhyolyte.] 



fine, and are sometimes distributed in the darker rock, somewhat as the spots 

 described by Bayley in the slates and quartzytes of Pigeon point,* but in general the 

 whiteness is coincident with certain of the laminations. It also surrounds the quartzes. 



Two sections. 



J//c. No. 140(11). Is almost identical with the general rock of the Great Pali- 

 sades. Its only difference is in the existence of a megascopic fluidal structure, coin- 

 cident with which are some lighter stripings. The feldspars are also not glassy but 

 opaque, with red and white products of decay. It has evidently been broken and 

 baked. Fine fracture-seams . cross it. These are sometimes rilled with quartz, but 

 more frequently with a darker-brown cement. In other fissures there is evidence 

 that the openings were the avenues of entrance of some decoloring foreign substance, 

 for along the fissure on either side is a narrow film of light red, or of pink. 



One section. 



M/c. No. 140(12). White, buff-white, or pinkish white. This rock possesses 

 all the characters, both megascopic and microscopic, of the others of this series, 

 except the color. By some means the coloring matter (ferric oxide) has been removed. 

 It constitutes but a small portion of the rock mass. It shows a coarse laminated 

 structure, due to flowage, the laminae being curved. 



Chemical iniiili/xix. An analysis of this rock (No. 140) gave the following result: 



SiO 2 - 69.60 



A1 2 O 3 11.49 



Fe 2 O 3 3.95 



FeO .60 



CaO 2.64 



MgO .71 



K 2 O 1.08 



Na 2 O 1.15 



H 2 O 8.55 



Total, 99.83 



Age. Cabotian; red-rock series. 



Remark, The whole of the specimens numbered 140, described above, are deriv- 

 atives from No. 139. They show gradations from the normal rock to the most varied, 

 of which probably 140(12) is the extreme. It is one of the most evident facts, all 

 along this coast, that fragments from a "red rock" are included in a coarse diabase 

 showing the later date of the diabase. The characters of the lowest visible portion of 

 the face of the Great Palisades, as expressed in the above descriptions, agree with the 

 field relations in pointing to the immediate subterposition of this diabase, and they all 

 point to the earlier date of this rock than that of the diabase. In other words, the 

 phenomena all warrant the supposition that the diabase itself refused the lower part 

 of the " red rock " and imparted to it more evident fluidal characters. The age of 

 the " red rock," here represented by No. 139, is hence considered Cabotian, and that 

 of the diabase a later eruptive of the Cabotian, but perhaps nearly cotemporary. 



* Bulletin cix. The eruptivo and sedimentary rocks of Pigeon point, p. 72. N. H. W. 



