890 



SCIENCE. 



[N. S. Vol. V. No. 127. 



truncated by this wearing action and at the 

 same time to have been elevated about 50 feet 

 within a comparatively short time. Near 

 Lomas a Tertiary plain 15 to 10 miles wide, 

 and reaching 500 to 600 feet above tide, be- 

 tween the mountains and the sea, has been so 

 recently reclaimed from the sea as to have 

 scattered over its surface not only beach peb- 

 bles, but frequent sharks' teeth and occasionally 

 jawbones of whales, from the latter of which 

 the villagers construct the crucifixes they always 

 plant upon some prominent headland. Further 

 inland there is a broad peneplain nearly 6,000 

 feet above the sea level, fringed by an old sea- 

 beach of rolled pebbles more or less covered by 

 beds of volcanic tuff. 



The geological formations along the coast 

 belt, as far as observed, are mostly granites and 

 diorites, in places surrounded by horizontal 

 or slightly crumpled beds from which fossils of 

 probable Miocene aud Pliocene age were ob- 

 tained. To the former apparently belong the 

 very considerable extent of petroleum-bearing 

 beds in northern Peru near Cape Blanco. The 

 main mass of the western crest of the Andes, 

 .where observed, consists of closely compressed, 

 infolded limestones, slates and conglomerates, 

 with intrusive andesites and other igneous rocks. 

 These sedimentary beds are thought to be of 

 probable Jurassic age, though no fossils were 

 obtained. 



The Telluride mining district, in the San 

 Juan mountains, was described by Mr. C. W. 

 Purington. It is situated in southwest Colo- 

 rado, on the line of the Sio Grande Southern 

 Railway. It is a mountainous region character- 

 ized by precipitous topography. The moun- 

 tains rise to 14,000 feet from a plateau of 7,000, 

 which bounds the region on the west. The 

 rooks are nearly flat-bedded sedimentaries of 

 Triassic, Jurassic and Cretaceous age, overlain 

 in the eastern part of the quadrangle uncon- 

 formably by a heavily bedded conglomerate, 

 i200 feet thick, above which lie 2,000 feet of 

 andesitic breccias, in part waterlaid, and still 

 higher 1,000 feet of volcanic flows, andesite 

 and rhyolite. Diorite stocks of large dimen- 

 sions have cut all the other rocks of the region 

 and are most recent in age. Surface denuda- 

 tion has exposed them to view. The centers 



of volcanic activity lies to the east of the 

 sheet. 



Several well-defined fissure-systems, due to the 

 action of extraneous forces, penetrate the rocks 

 of the region. The systems are characterized 

 by the alternation of widely and narrowly 

 spaced zones of fissures. The zones of nar- 

 rowly spaced fissures vary from one to ten feet 

 in width, aud it is along these that the work- 

 able veins are found. Relative movement of 

 the walls of the closely fissured zones, accom- 

 panied by trituration of the included rock, de- 

 veloped open space which the ore now occupies. 

 The veins carry gold, mostly free, but in part 

 combined with metallic sulphides, silver mostly 

 in galena and freibergite, less frequently as 

 stephanite, pyrargyrite, polybasite, etc. Beside 

 iron, lead, copper and zinc sulphides, there oc- 

 cur as gangue, predominating quartz, carbon- 

 ates, barite, fluorite, sericite and other miner- 

 als in small amount. Gold and silver veins 

 occur closely associated. Accompanying the 

 veins the wall rocks are altered, and impreg- 

 nated with iron pyrite, occasionally auriferous. 

 The values vary between wide limits. They 

 must be given in more detail than is possible 

 here. The veins show remarkable continuity 

 in length, one having been profitably worked 

 for a distance of more than two miles. 



The ore is of Tertiary age, is of deep-seated 

 origin, and has been deposited from solutions; 

 $20,000,000 is a low estimate for the product of 

 the district. It has steadily increased in im- 

 portance since 1875, and very rapidly within 

 the last five years. Formerly silver was the 

 principal product ; now much the larger output 

 is in gold. W. F. Moesbll. 



U. S. Geological Survey. 



NEW YORK ACADEMY OF SCIENCES — SECTION 

 OP GEOLOGY, MAY 17, 1897. 



The first paper of the evening was by Mr. D. 

 H. Newland, entitled ' Occurrence and Origin 

 of the Serpentines near New York. ' Mr. New- 

 land spoke of the occurrence of Serpentines in 

 the vicinity of New York and classified them 

 according to origin into two probable divisions ; 

 one including those from New Rochelle and 

 Hoboken, possibly derived from metamorphosed 

 igneous rocks, and second, those from the other 



