PETROGRAPHICAL PROVINCE OF ESSEX COUNTY 1 1 7 



my specimen agrees with his descriptions, especially as to the 

 megascopical appearance, the feldspars and the flow structure. 

 But there is a marked discrepancy in the colored components, 

 and it is evident that here also the dike varies in character in 

 different parts, assuming that the two specimens came from the 

 same dike. From analogy with the Andrew's Point dike, it 

 would seem that Rosenbusch's specimen came from the border, 

 while mine came from near the center. 



The rock is rather dark gray, fine-grained, and, in my speci- 

 men, with little suggestion of silky luster. The tabular alkali- 

 feldspar phenocrysts are identical with those described by 

 Rosenbusch. This author speaks of a blue glaucophane-like 

 hornblende as the only colored component. In my specimen 

 this occurs very sparingly, its place being taken by a highly 

 pleochroic, peculiar olive-green hornblende, bright green aegi- 

 rite grains, and flakes of a greenish-brown, intensely pleochroic 

 biotite. Generally these are scattered uniformly through the 

 section, but in places one or the other predominates. A few 

 phenocrysts of colorless diopside are seen, surrounded by a nar- 

 row border of aegirite. A number of fair-sized titanite grains 

 and a few apatite needles are present, but quartz is wanting. 

 Flow-structure is very pronounced, and is well brought out 

 between crossed nicols, on account of the highly tabular devel- 

 opment of the groundmass feldspars. 



The last of the solvsbergites to be described was found as 

 blocks in a wall along the back road southwest of Bass Rocks. 

 It is very dense and compact and of a deep bluish-gray color. 

 Under the microscope no phenocrysts are visible, and practically 

 the only colored component is a deep blue glaucophane, which 

 occurs in abundant needles or stout prisms. There are also 

 present, in extremely small amount, small grains of colorless 

 diopside, but no aegirite, biotite, or green hornblende. The 

 rock is chiefly remarkable for its colorless base, which is 

 composed of alkali-feldspar, with considerable quartz — enough 

 to justify the name quartz-solvsbergite. These are partly 

 irregularly granular, but also form small patches with micro- 



