336 PEOCEEDINGS OP THE GEOLOGICAL SOCIETY. [JuDG 9, 



3. On the Caeatal Gold-field. 

 By C. Le Neve Fostee, B.A., D.Sc, F.G.S. 



[Abridged.] 



The Caratal goldfield, for our knowledge of wliicli we are indebted 

 to Dr. Plassard, is situated in Yenezuela, about 160 miles in a 

 straight line east-south-east of Ciudad Bolivar or Angostura, the 

 capital of the State of Guayana. It lies about 100 miles south of 

 the River Orinoco, about seventy-five miles up from the principal 

 mouth. 



Before entering upon a description of the various kinds of gold- 

 deposits, I must give a short general sketch of the geology of the 

 district. 



The country between Ciudad Bolivar and Pastora consists almost 

 entirely of gneiss, with some mica-schist and hornblende -schist, and 

 a little granite. All three varieties of rock are seen at Ciudad Bo- 

 livar itself. From Ciudad Bolivar to the Caroni there is a gently 

 undulating savannah showing outcrops of gneiss as far as the neigh- 

 bourhood of the Arasiama ridge, which is formed of itaberite. About 

 Arasiama, and on both sides of the Caroni near Guri, the strike of 

 the gneiss is, roughly speaking, east and west. 



Beyond Charapo there is some hornblende -schist striking E. 15° N. 

 in some of the land which forms the watershed between the basin 

 of the Orinoco and that of the Essequibo. Where the road crosses 

 it, the watei'shed is not more than abont 1100 feet above the sea- 

 level. 



Further east, at Limones, I saw granite ; but the greater part of 

 the country consists of gneiss, which now gets a strike of N. 18° W. 

 to jIST. 15° E. Both east and west of the Oronato I found horn- 

 blendic schist, striking N. 10° E., N. 45° W. 



In crossing the Guatapolo I noticed a dyke of porphyrite re- 

 sembling some of the Cornish elvans, and remarkable for the well- 

 crystallized quartz which it contains. 



Before arriving at Pastora the series of schists and slaty rocks, 

 which continue into the Caratal district, make their appearance ; 

 near Pastora there are siliceous schists striking N. 45° "W., N. 60° W., 

 IS". 70° W. ; and at Caratal itself these rocks are often a fine-grained 

 clay-slate like some of the Cornish " killas." At other times the 

 rock is much coarser ; and a very talcose variety frequently occurs. 

 As a rule, these slaty rocks are much decomposed. The decom- 

 posed schist forms the " bed-rock " in many of the alluvial diggings, 

 and is known to the miners as " cascajo." Besides these slaty 

 rocks, there are large outcrops of a felstone ; but I cannot say 

 whether it is intrusive or interbedded. This felstone is the "blue- 

 stone " of Dr. Stevens *. It is a compact grey, bluish-grey, or 

 greenish -grey rock, often containing small crystals of iron pyrites, 

 the " mica " of the miners. The schistose rocks have, roughly 

 speaking, an east and west strike, with a varying dip. 



* ' Scientific American,' 25th Not. 1868, and ' American Journal of Mining,' 

 1st Aug. 1868. 



