﻿H. M. Seely — Genus Strephochetus. 31 



The resemblance between the volcanic products of the two 

 regions is strikingly brought out by a comparative study of the 

 basalts; in many instances the basalts found in Salvador exhibit 

 an identical structure with those described from the Great 

 Basin.* 



The transition from olivine-bearing basalts to hypersthene- 

 bearing andesites is quite the same, and moreover holds equally 

 true for the volcanoes of Oregon, California and Washington 

 Territory.! 



Again, the relations shown to exist between the orthorhombic 

 and monoclinic forms of pyroxene in Nevada holds true in the 

 minutest details for the rocks of Salvador. The former yields 

 more readily to the forces of decomposition than the latter, so 

 that many thin sections show fresh augite and partially altered 

 hypersthene, and others unaltered augite with wholly decom- 

 posed hypersthene. In no case had the augite been attacked 

 while hypersthene remained unaltered. 



The following list of localities includes those from which the 

 better characterized rocks have been collected : 



Basalt, from volcano of San Miguel ; volcano of Izalco ; 

 Carancasuna; Quebrada de San Bartolo ; San Ysidro Koad ; 

 Cerro La Tabla ; La Joya, Valle de Zapote. 



Pyroxene- andesite, Cerro de Cunchique ; Sumpul River, near 

 Llano Malo ; Sumpul River, between Oja del Sal and Las 

 Flores ; Duron's Mine ; Bosque Mine. 



Hornblende-pyroxene-andesite, volcano of Ilopango ; bank near 

 San Jacinto ; San Sebastian Quarry ; Canon of the Tamulasco, 

 below Las Minas. 



Hornblende-mica- andesite, quarry, Cerro la Tabla. 



Dacite, Cerrito de Avila ; Llano de la Hacienda, one mile 

 S.E. of San Ysidro ; San Sebastian, columnar rock ; Santa 

 Rosa road, three or four miles east of Jocoro ; Western Bluff 

 of Cerro La Tabla. 



Art. V. — The Genus Strephochetus : — Distribution and Species; 

 by Henry M. Seely. 



1. Distribution. — In communicating to this Journal, Novem- 

 ber, 1885, the existence of the fossil sponge, Strephochetus 

 ocellatus, the writer named the towns Addison and Bridport 

 in Vermont and Crown Point in New York as localities where 

 it had been found. Further observation shows the existence of 



*F. Zirkel, Microscopical Petrography, Washington, 1876. Hague and Id- 

 dings, this Journal, vol. xxvii, JuDe, 1884. 



f Hague and Idaings, this Journal, vol. xxvi, Sept.; 1883. J. S. Diller, this 

 Journal, vol. xxviii, Oct., 1884. 



