Geology and Mineralogy. 495 



Lyceum of Natural History of New York, pp. 155 and 159. He 

 states that the specimens in some layers of the limestone are very 

 numerous: 326 entire specimens were counted in a space meas- 

 uring 30 feet by 40 ; and, of these, all but 8 lay with the back 

 downward, the position which exuviae of the concave form in Ce- 

 raurus would take. Their length varies from y^ of an inch to 2 

 inches. The separated heads are found in immense numbers, and 

 the surface of the rocks is sometimes nearly covered with them. 

 10. Glacial phenomena in Jefferson Co., New — ^ ■ 



the north, (dist 

 ding with the : 

 tween Theresa and liedwood, an^ with the general course of In- 

 dian River. The course is the same as that observed by Emmons 

 near Watertown. Well characterized roches rnoutonn'ees, with 

 their steepest side facing southwest, occur near Theresa. Mr. 

 Lloyd also describes a pot-hole in the Laurentiau granite which is 

 29 feet deep and 7 to 10 feet in diameter. 



11. Origin of the Porphyry of Marblehead, Mass.—Mx. T. T. 

 Bouve, in the Proceedings of the Boston Society of Natural His- 

 tory for January 19, 1876 (xviii, 217), discusses the origin of the 

 red porphyry and red felsyte rock of the vicinity of Marblehead, 

 and proves it to be of metamorphic origin. The felsyte has long 

 been known to contain disseminated grains or fragments of quartz. 

 He states that in 1862 he observed that the felsyte, near Hing- 

 ham, was in part pebbly and slaty, and graduated into a conglom- 

 erate, and had evidently been derived from the alteration of the 

 conglomerate. His observations since have confirmed this con- 

 clusion. [A fine series of specimens was exhibited, illustrating 

 the transitions.] 



Mr. Bouve stated further that he was disposed to include among 

 the rocks having the same origin some, at least, of the underlying 

 syenytes. The succession of rocks as given by others, is— (1) con- 

 glomerate; (2) compact feldspar or felsyte, gradually passing into 

 porphyry ; (3) porphyry, gradually passing into a rock between 

 porphyry and syenyte ; (4) syenyte ; and this relation of the beds 

 Mr. Bouve observes, is itself probable evidence that the causes 

 that led to the changes in the higher portions of the series affected 

 all, though in varying degrees. 



The reading of Mr. Bouve's paper was followed by remarks by 

 Mr. Hyatt, sustaining the view that had been presented respect- 

 ing the origin of the^porphyry. Among his facts he stated that 

 at one point on the ocean side of Marblehead Neck, the variegated 

 conglomerate is altered to compact light-colored felsyte in one di- 

 Kiction, and in another to a true deeply colored porphyry, con- 

 taining distinct crystals of feldspar ; and that the included pebble 

 "- 'be traced until it becomes, without any change of 



e spot in the light felsyte matrix, the interior last 

 iginal characteristics. 



