Vol. 56.] LA SALINE (NORTHERN JERSEY;. 321 



mica makes the rock appear quite dark, but here it is more evenly 

 distributed. This is also distinctly fine-grained. Again in a few yards 

 the rock is exposed both coarse and porphyritic, but still containing 

 some quantity of mica. Some 5 or 6 yards from the peppered rock is 

 a very irregular dark patch, measuring roughly 24 by 20 inches, and 

 containing much mica. A thin section shows this to exist in well- 

 formed flakes, commonly '03 inch across, dark straw-yellow in colour, 

 with very strong absorption. There are also idiomorphic hornblendes 

 now greatly altered, but retaining crystal-outlines ; and rather dusty 

 quartz, like that in the surrounding rock, is abundant. The felspars 

 consist of orthoclase with microperthitic intergrowth, and some 

 quantity of plagioclase having low extinction-angles. The mica, in 

 appearance and mode of occurrence, does not differ from that of the 

 rocks close by. 



This patch, inclusion, or segregation has no very distinct edges, 

 but a conspicuous shading-off of the dark minerals into the surround- 

 ing rock is not seen. Outlying patches are found close by, apparently 

 separate from the main mass. 



The evidence afforded by this group of rocks alone might perhaps 

 point to a certain irregularity of composition in an acid magma, and 

 some segregation of the more basic materials during consolidation. 

 But they do not stand alone : on the upper part of the cliff at the 

 western end of the Bay, i.e. at that nearest Sorel Point, a fine-grained, 

 rather dark rock appears above the surface in outcrops mingled with 

 others of a more granitic texture. (Some of these are possibly the 

 * diorite ' mentioned by M. Noury.) These greatly strengthen the 

 suspicion, as to the true origin of the mica in the rocks of the shore, 

 which the nearness of the mixed and altered rocks of Sorel Point 

 would of itself have raised. There can be no doubt that in this 

 corner of the Bay granite occurs, containing material absorbed 

 from a diabase (dolerite), probably also diabase impregnated by an 

 acid magma. Under the microscope we find remnants of greatly 

 altered diabase, whose hornblendes are illshapen and associated with 

 biotite teased out into an embedding matrix of quartz-grains and 

 felspars, for the most part orthoclase, testifying clearly to the non- 

 homogeneous nature of the rock. Through the more acid meshwork 

 — which contains large orthoclases — multitudes of colourless acicular 

 crystals, referred to sillimanite, are scattered. Not included in the 

 section, but common in the rock, are groups of quartz-grains 

 surrounded by narrow hornblende-rings. These are also a feature in 

 the similar rocks from Sorel Point. 



A fragment of a fine-grained, non-porphyritic, speckled grey-and- 

 white rock, measuring 9 by 4 J inches, which is included in the coarse 

 aplitic rock of the shore below, may possibly be allied to such mixed 

 rocks in its mode of origin. In a thin section are seen numerous 

 lath-shaped opaque felspars surrounded by clearer zones, apparently 

 of an acid plagioclase, a few irregular crystals of orthoclase, flakes of 

 brown mica and dark-green hornblende, and some quantity of quartz. 

 The last-named occurs sometimes in grains, which in one case 



