1914.] NATURAL SCIENCES OF PHILADELPHIA. 7 



an offshoot which extends into a parallel crack in the granite. A 

 block of granite which has been picked up by the molten dike rock 

 is exposed in the interior of the latter. 



East of this is an extensive intrusion of quartz porphyry, so classed 

 from the general characteristics of the whole mass, rather than from 

 the microscopical examination of individual sections, some of which 

 would otherwise rank as fine-grained granites, while others show a 

 few phenocrysts and patches of micro-pegmatite. Within this 

 intrusion are segregations containing crystals of hornblende several 

 inches long and large masses of blue quartz. It has been injected 

 with diorite, but as it does not split in straight lines like the granite, 

 no regular dike is exposed. The diorite has forced its way irregularly 

 among the fragments of the older rock, some of which are included 

 in it. The diorite consists of a fine-grained mixture of hornblende, 

 biotite, and triclinic feldspar, with a few phenocrysts of zoizitised 

 plagioclase and occasionally a small one of light colored pyroxene. 

 It is intersected by numerous small white veins, no doubt of secondary 

 origin, and consisting in one section examined of feldspar, both 

 orthoclase and plagioclase, and light colored pyroxene. 



To the south, the dike of solvsbergite, which crosses the point, 

 again appears, and further on a sharply defined dike of quartz 

 porphyry several feet thick. Still further south are three small 

 dikes of diorite, differing from that at the point in several minor 

 respects. There is but little biotite, and the hornblende is of a bluish- 

 green color. No veins were noted, and the smallest dike, which is 

 l3ut a few inches thick, is very fine-grained and free from phenocrysts. 

 They are probably all derived from the same source. 



Beyond them comes another series of dikes, all no doubt of similar 

 origin. They are, respectively, two to three inches, twenty-eight 

 inches, sixteen inches, and eighteen feet in thickness, the latter just 

 below the Ocean View Hotel, while further on is still another nearly 

 as large. The larger dikes are typical fully crystallized diabases, 

 coarser or finer grained according to size of dike, with unaltered 

 constituents and basaltic texture near the contacts. The two- to 

 three-inch dike is basaltic throughout. It passes close to a swimming 

 pool blasted out of the rocks, and is visible over the sloping shore 

 for a couple of hundred feet, occupying a crack in the granite as 

 straight and sharply defined as if cut with a knife. 



The sixteen-inch dike is admirably adapted for illustrating the 

 effect of quick or slow cooling on an igneous rock, as it has an offshoot 

 or branch, three-eighths to two inches thick, extending into the 



