PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 405 



Aporhyolyte. Conglomerate. Diabase.] 



region. It certainly produced in a belt of varying width and volume an intermediate 

 rock (No. 531) caused by the reaction of the acid element on the diabase itself. This 

 diabase and its geognostic relations are more fully treated in Part I, of this volnme. 



N. H. w. 

 No. 533. APORHYOLYTE. 



"Rock of the Great Palisades. (Compare No. 139.)" 

 I\cf. Annual Report, x, page 41. 



A reddish-brown rock, hard, compact and aphanitic. It is thickly strewn 

 with small phenocrysts of quartz and a gray to pinkish feldspar. 



M/i'. The section contains two quartz phenocrysts and one small feldspar in 

 a groundmass which shows poikilitic quartz areas of considerable size. The section 

 furnishes an excellent example of these poikilitic quartzes in a devitrified rhyolite. 

 (Compare No. 68.) Mat/in'titi' and much hematite are present in minute particles 

 throughout the rock, and also in larger grains. A feature of the section is a small 

 quartz vein which crosses it and which cuts directly through one of the quartz 

 phenocrysts. In this crystal the vein is cloudy, but the quartz deposited in the vein 

 has the same orientation as the phenocryst. Another section, made later, shows 

 essentially the same features. 



Two sections. 



Age. Cabotian. u. s. G. 



No. 534. CONGLOMERATE. (Red.) 



At one mile east of Manitou river. The same is seen at the mouth of Manitou river. 

 Ref. Annual Report, x, page 42. 



Meg. Easily crumbling, the cement being principally of calcite. Some of the 

 pebbles are about an inch in diameter, and from that size they grade downward to 

 mere sand, yet the whole mass is composed of eruptive materials, of which the most 

 of it was originally porous. It appears to have been produced entirely by waste 

 from an amygdaloidal lava. 



No section. 



Age. Potsdam. N. H. w. 



No. 535. DIABASK. ( Mesolite, scolescite* and tJiomsoiiiic fnnii<i<lah>i<l.) 



Terrace point. (See Nos. 1G3A and 193.) 



Ref. Annual Report, ix, page 51; Annual Report, x, page 42; American Geologist, vol. xxii, page 347, 

 December, 1898. 



MCI/. Amygdaloidal diabase, containing many zeolites which have been widely 

 distributed as thomsonite. 



Mic. A fine large section made by Marchand shows the nature of this rock in 

 a beautiful manner. As a whole the rock is ophitic and amygdaloidal, but the small 



*If, according to Dana, this name is derived from cwni^f , the proper spelling is neither scolecite, preferred by him, nor 

 scolesite, used by Lacroix, but scolescite, the letter f being derived from a Doric composition of m . 



