PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 211 



Aporhyolyte.] 



Chemical analysis. The following analysis was made by Prof. J. A. Dodge and was first published in the 

 Thirteenth Annual Report, page 100 (No. 158): 



SiO 2 76.68 



Al a O s 12.14 



Fe 2 O 3 3.16 



FeO .52 



CaO .25 



MgO .26 



K 2 3.53 



Na 2 O 1.06 



H 2 1.66 



Total 99.26 



The analysis shows this rock to be higher in Si0 2 and lower in CaO than most 

 of the acid rocks of the Cabotian, and the amount of K 2 0, in reference to Na 2 0, is 

 greater than in many of these rocks, which frequently have a larger amount of Na 2 

 than of K 2 0. 



Age. Cabotian. u. s. G. 



No. 140. APOKHYOLYTE.* 



From the contorted and fluidal portions of the Great Palisades near the water level. 



Kef. Annual Report, ix, pages 21, 35, 36; Annual Report, x, pages 38, 110; Annual Report, xiii, pages 100 

 (No. 159), 103; Bulletin viii, page xxxiii; figure A of plate 44, Bulletin cl, U. S. Geol. Survey, was made from 

 No. 140(1). 



. The rock here has been twisted and recurved so as to defy description. 

 Large hardened masses or concretions occur in the fluidal portion. The whole of it 

 contains the translucent crystals common in the bulk of the rock above, and also 

 one Or more species of feldspar. Some of it is red, some green, some brown, some 

 dirty white, or buff; some is laminated, and some is massive, with a conchoidal frac- 

 ture. The matrix of the crystals and the parts between the translucent laminae are 

 not crystalline, but seem to have been perfectly molten, though probably cooled 

 rather suddenly. These laminated parts, and other (brownish) streaked portions, 

 appear to have been drawn out in a streamed structure. The most careful examina- 

 tion was made of No. 140(7), but all the specimens numbered 140 bear a general 

 resemblance. The green rock, associated with No. 140, is described under Nos. 136 

 and 137. Eock No. 140 is the same as Irving's No. 876. (U. S. Geol. Survey, Mono- 

 graph v, page 109. Compare, also, Nos. 812 and 813; also, No. 162.) 



Mir. No. 140(1) is light red and (jnuj, and is laminated by a distinct fluidal 

 structure, the thinnest laminae being less than a thirty-second part of an inch in 

 thickness, and some of the red, amorphous rock being simply striped with a translu- 

 cent layering, or with a buff-white substance which appears more abundantly in 

 some places, as in No. 140(12). The fluidal structure curves round the feldspar and 

 quartz phenocrysts, and sometimes presents a perlitic structure, as represented in 

 No. 140(7). The quartzes are corroded, and the reddened magma enters them some- 



* As collected the specimens bearing this number represent a varied lithology, and for the purposes of description they 

 are here further designated by subordinate numbers in parentheses. 



