PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 275 



Basalt. Diabase.] 



Nic. The elements in the slide are hardly differentiated. The feldspars are 

 indistinctly combined in the matrix. There are minute polarizing spots, but without 

 the crystallographic outlines of feldspar. This may have resulted from the consoli- 

 dation of a tuff. In another slide the rock appears the same as in No. 237, but has 

 larger amounts of hematite; also calcite and biotite. 



Two slides. 



Aye. Cabotian. N. H. w. 



No. 241. BASALT (ivith olivine). 



Same rock, same place, but nearly black. Cannot be distinguished from No. 

 237, except that the feldspars are not so well formed as to crystalline boundaries. A 

 minutely fine basalt. 



One section. 



Af/c. Cabotian. N. H. w. 



No. 242. DIABASE (lultli quartz). 



From a dike cutting Nos. 237-241; 100 feet wide, running nearly east and west. 

 Ref. Annual Report, ix, pages 59, 60. 



Mt'ij. Grain medium in size. Some feldspars being conspicuous and striated. 

 Grayish-brown rock. 



Mic. The feldspar is of two periods of generation, the earlier one having 

 twinning after the Carlsbad law, the two individuals being twinned after the albite 

 law. A section of such a twin is perpendicular to n p (a) and has extinction at 56, 

 which indicates a feldspar near anorthite. Another section is yellow between crossed 

 nicols, and happens to be cut perpendicular to n m (b), showing the thickness of the 

 slide at this place is about .0525 millimeters. It varies, however, being in other places 

 .0325 millimeters. 



There is considerable quartz in the rock, in independent grains, yet in some 

 cases it is minutely distributed through other minerals in the form mentioned in No. 

 225, forming a micropegmatyte. 



Auyite is not abundant nor well preserved. It is granular amongst the feldspars 

 rather than ophitic, causing the rock to take on the character of a granular gabbro, 

 and identical with the rock of Nos. 233 and 234. 



One section. 



A<jc. Manitou. 



Remark. Nos. 232 and 235, and their modifications to No. 241, run under No. 

 230, the Eastern Palisades, and below the red rock of the point east of the Eastern 

 Palisades. These are basic surface flows, and the Eastern Palisades are of an acid 

 effusive. N. H. w. 



