498 Pirsson and Washington — Geology of Weio Hampshire. 



dioritic-appearing rock in which the large poikilitic horn- 

 blendes are much restricted in amount or even entirely dis- 

 appear. There is also considerable variation in grain. One 

 specimen shows a granular rock with black and white minerals 

 evenly mixed in very nearly equal amounts, the size of grain 

 from 2-4 mm . The white mineral is feldspar, the black mostly 

 hornblende, with some angite and here and there bronzy 

 lustered biotites. In other places the rock is the same but of 

 much finer grain. Under the microscope the same minerals 

 are seen as in the gilfordal camptonose but in more variable 

 amounts. Biotite is generally much more abundant; the 

 brown hornblende in places yields to a green variety. Other- 

 wise the minerals need no especial comment. Their relative 

 proportions are variable and in one case the passage into a dis- 

 tinctly salic phase was noted, the rock containing an excess 

 of feldspar, much of which is alkalic. Detailed study and 

 analysis of the different facies at this place would undoubtedly 

 show varieties bordering upon, or in, monzonase (monzonite, 

 diorite and perhaps akerite of the older classifications), but 

 these facies are of such restricted volume and confined to such 

 a limited area, and play so small a role in the general petrog- 

 raphy of the region, that it has seemed scarcely of value to 

 undertake a complete chemical and petrographic investigation 

 of them. They are so involved with what we consider the 

 later irruptions of persalic magma described under the head- 

 ing of breccia, that from the field exposures nothing more 

 definite can be worked out than that they are distinct differ- 

 entiation facies of the camptonose as stated above. 



Hampshiral camptonose (camptonite) . 



Basaltic dikes of salfemic rocks are rather numerous in the 

 area and a number of localities in which they have been found 

 are mentioned in our previous paper. They are all composed 

 of rocks made up of a brown barkevikitic hornblende and 

 plagioclase which fall under camptonose or adjacent subrangs, 

 or are camptonites in the older systems. One of these which 

 affords the best preserved material occurs on the southwest 

 side of Mt. Belknap, near the top, cutting a steep slope of 

 syenite which is well exposed above the hillside pasture fields, 

 the dike is about 3 feet wide with a pronounced columnar 

 structure and is exposed for about 100 yards. A specimen of 

 this was selected as a type for detailed study, measurement 

 and analysis. 



Megascopic. — Phanerocrystalline to aphanitic ; very dark 

 stone-gray ; thinly sprinkled with minute white dots 0*25- 

 l*00 mm in diameter (calcite fillings) ; the compact to fine- 

 grained mass abundantly filled with slender dark glistening 



