chap. xiii. Crystalline Rocks of. 429 



five miles west, and for about seventy miles north of 

 Maldonado : near this town, there is some common 

 gneiss, and much, in all parts of the country, of a 

 coarse-grained mixture of quartz and reddish feldspar, 

 often, however, assuming a little dark-green imperfect 

 hornblende, and then immediately becoming foliated. 

 The abrupt hillocks thus composed, as well as the 

 highly inclined folia of the common varieties of gneiss, 

 strike NNE. or a little more easterly, and SSW. Clay- 

 slate is occasionally met with, and near the L. del 

 Potrero, there is white marble, rendered fissile from the 

 presence of hornblende, mica, and asbestus ; the cleavage 

 of these rocks and their stratification, that is the alter- 

 nating masses thus composed, strike NNE. and SSW. 

 like the foliated gneisses, and have an almost vertical 

 dip. The Sierra Larga, a low range five miles west 

 of Maldonado, consists of quartzite, often ferruginous, 

 having an arenaceous feel, and divided into excessively 

 thin, almost vertical laminas or folia by microscopically 

 minute scales, apparently of mica, and striking in the 

 usual NNE. and SSW. direction. The range itself is 

 formed of one principal line with some subordinate 

 ones ; and it extends with remarkable uniformity far 

 northward (it is said even to the confines of Brazil), in 

 the same line with the vertically ribboned quartz rock 

 of which it is composed. The S. de las Animas is the 

 highest range in the country; I estimated it at 1,000 

 feet; it runs north and south, and is formed of feld- 

 spathic porphyry; near its base there is a NNW. and 

 SSE. ridge of a conglomerate in a highly porphyritic 

 basis. 



Northward of Maldonado, and south of Las Minas, 

 there is an E. and W. hilly band of country, some miles 

 in width, formed of siliceous clay-slate, with some quartz, 

 rock and limestone, having a tortuous irregular cleav- 



