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PROCEEDINGS OE THE GEOLOGICAL SOCIETY. 



[Nov. 21, 



35. Similar slates ; still more altered 



( Tentaculites supremos and a Cup- 

 | coral ; also several indistinct fossils, 

 ■{ amongst which many bodies about 

 | 3 to 4 inches long, looking like 



^ Orthoceratites. 



36. Similar strata, whitish brown or pur- 

 plish 



C Homalonotus Linares, Tenta- 

 \ culites supremus, Ctenodonta, and 



[ a Cup-coral. 



This bed is the lowest in position of the strata here examined ; and, 

 being tilted up as shown in Section No. 1, it forms the summit or 

 knife -like ridge of this mountain which separates the barren alpine 

 plains of the Puno, on the west, from the verdant tropical regions of 

 the Yungas, to the eastward. On a clear day the line of bedding of 

 the last-mentioned strata can easily be followed by the eye, up to the 

 very highest point of the ridge itself, the steep and highly inclined 

 sides of which prevent the perpetual snow crowning its top from 

 showing itself as a continuous envelope, and only allowing it to 

 lodge itself in the hollows, crevices, and offsets formed by the strata, 

 which, as it were, prop up its summit. 



The section across these beds shows also that the valley of Millepaya 

 is merely due to erosion, and not to a fault or break in the stratifi- 

 cation as its peculiar configuration might lead us at first to suspect; 

 it becomes gradually narrower as it ascends, and loses itself as a 

 ravine in the western slope of Illampu. The following observations 

 of strike and dip were taken : — Bed No. 2 : Brown micaceous slates, 

 N.5°W.,dip 50°W. Bed No.34 : Hard, white, altered slates, N.25°W., 

 dip 32° W. Bed No. 35 : Hardened brownish-white clay-slate, 

 N. 10° E., dip 35° W. Other observations gave the same strike ; 

 but the dip was found respectively to be 25°, 30°, 38°, 42° W. ; and 

 still higher up in this bed the observed strike was N. 10° E., and the 

 dip 40° W. 



In these slates abundant furrows and deep grooves were observed, 

 sometimes very deep, and miming from N. 80° E. to E. & "W. ; also 

 veins of spathic iron-ore, arsenical pyrites, and auriferous pyrites ; 

 veins of mispickel or sulpharsenide of iron were found running 

 N. 50° E. to N. 60° E., and dipping to S.E. at an angle of 75°, cutting 

 through and altering the strata. 



On the sides of this mountain are also found veins of argentiferous 

 galena, gold-bearing quartz, and metallic bismuth, the latter some- 

 times in large masses, occasionally faced, or incrusted on the sides, 

 with metallic gold, sometimes in crystals. Iron-ore is also abundant*. 



About ten miles to the south of Millepaya, on the west slope of 

 Illampu, at Capara, I found, in the loose blocks of soft blue slate there, 

 Orthis Aymara, a trilobite (probably Homalonotus), a Cup-coral, and 

 abundant Annelid-burrows, also a Trilobite (possibly a Calymene) 

 in hard grauwacke. 



Still further to the south, at Umapozo, I found Ctenodonta (Nucula), 



* I was informed by M. Villamil of a recent discovery of anthracite-beds in 

 these strata ; but, as yet, I have not received any satisfactory confirmation of the 

 tame. 



