1884.] Microscopic Structure of some Rocks from Ecuador. 401 



base, containing minute crystallites, probably for the most part felspar, 

 but perhaps also a pyroxenic mineral, with rods of opacite and with 

 ferrite staining. In this occur crystals of plagioclastic felspar, not 

 generally exceeding '03 inch, agreeing in general character with those 

 already described, but perhaps more frequently containing enclosures, 

 and "dirty looking," together with a pyroxenic mineral. The crystals 

 of this are not very characteristic, but 1 think both augite and hyper- 

 sthene can be identified. The other specimen is a small, rather rounded 

 fragment, of a darker and more vesicular lava than the last, but with 

 the usual whitish felspar crystals. The ground-mass, except in the 

 thinnest sections, is practically opaque, but in those it is seen to be a 

 light brown glass studded with crystallites, as already described, and 

 containing specks of opacite. There are the usual larger crystals of 

 plagioclastic felspar, perhaps rather cleaner tha*n in the case of the 

 other rock, with crystals of a pyroxenic mineral,. among which, I think, 

 both the monoclinic and the orthorhombic species may be recognised. 

 Thus both these rocks from Cotocachi appear to be hyperstheniferous 

 augite-andesite. 



Sara-urcu. 



" Few references to this mountain will be found in the works of 

 previous travellers in Ecuador. Beiss and Stiibel appear to have seen 

 it, for in their list of altitudes they mention that they made its height 

 6,800 metres (15,748 feet) by A in the year 1871, but they seem to 

 have been doubtful about their determination, and do not enter that 

 or any altitude in their " Tabla comparatiua." They quote from 

 Villavicencio, who in his Geografia de la Republica del Ecuador (p. 52) 

 gives its height as " 6,210 varas sobre el mar," upon which Messrs. 

 Reiss and Stiibel remark " es probable que estas alturas no son sino 

 avaluaciones aproximativas 6 reducciones inexactas; pero no resul- 

 tados de trabajos originales " (reckoning the vara at 2'782 English 

 feet, 6,210 varas are equal to 17,276 English feet). 



" Villavicencio quotes from Velasco passages to the effect that this 

 mountain is a volcano that formerly emitted fire and has latterly 

 ejected ashes, which have produced consternation in Quito, from 

 which city the mountain is distant 35 miles to the east. I give the 

 original below.* The results of my observations show that the moun- 

 tain is not a volcano ; that it is only 15,502 feet high ; that it cannot 



* " Segun refiere el P. Velasco en su historia de Quito, este volcan ha arrojadq 

 llamas por dos veces ; mas, en estos ultirnos afios, ba arrojado gran cantidad de 

 cenizas voicanicas, por Diciembre de 1843, i por el mismo mes, en 1856. La primera 

 de estas erupciones dnrd dos dias, i puso en mticho consternacioa a los habitantes de 

 Q.uito, i a sus pueblos circumyecinos. La altura de esta montana es de 6210 varas 

 sobre el mar. . . . Esta situado a 35 millas E. de Quito." Villavicencis, 

 pp. 52-53. 



