484 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



east half a mile to a point beyond the Moody Corners M'ood road it will be 

 seen to be bordered on the south by a rounded mass of diabase litholog-ically 

 different from anything found elsewhere in the valley, and very peculiar. It 

 has along dike projecting to the east, and is thus paddle-shaped and rudel}^ 

 resembles the much larg-er Black Rock core. It is an aphanitic diabase, 

 which is full of grains of quartz, microcline, orthoclase, etc. — so full that in 

 breaking hand specimens from every ledge aci'oss its width, 650 feet, not 

 one was found that did not contain many grains. It is as if the lava had 

 broken up through unconsolidated sandstones or flowed over beds of sand, 

 taking up a great quantity of the latter in its progress ; and as the tuffs con- 

 tain a certain quantity of the same granitic sand, and as this had often been 

 relied on as a means of distinguishing the tuff from weathered outcrops of 

 the trap in the field, a new tiifficulty was added, and weathered outcrops 

 of this trap.were with great difficulty distinguished. Indeed, in my first sec- 

 tion across this area I was in great perplexity, and the peculiar pitchstone- 

 like appearance of the rock, quite new in this region, added thereto. Still, I 

 decided before cutting sections that the rock must be a lava and not a tuff. 



PETROGRAPHICAL DESCRIPTION. 



The specimens described here were taken on a section thi'ough the 

 middle of the dike, where a wood road goes north a short (hstance east of 

 Moody Corners and crosses the brook where a branch enters it. From this 

 point the first outcrop of the trap is visible, and going north across a cleared 

 area and then a short distance thi'ough the woods to a second cleared field 

 one finds abundant exposm-es of the trap, and to the north long ridges of 

 the sandstone apjjear. The first section was taken from the north cleared 

 field, 23 feet south of north border of the diabase. It is a clear, black, 

 aphanitic rock of unusual freshness and slightly pitchy luster, and contains 

 in great quantity inclusions of granitic quai-tz, and rarely orthoclase, of the 

 same size as the grains in the adjacent sandstone (up to 5°"°). As many as 

 tlu-ee or four to a square centimeter occur, and the lens shows many more of 

 smaller size. Fragments of a glassy triclinic feldspar, perfectly fresh, and 

 the larger groups of plagioclase of earlier consolidation are also visible. 

 The quartz is coloi'less or slightly blue, of strong greasy luster, without 

 fissures and with rounded outline, or much fissured and then yellowish. 

 A single grain, 5"'" square, was made up mostly of a flesh-colored feld- 

 spar, but nearly a quarter of its mass was of the same greasy, bluish quartz. 



