76 STRATA Of GKETSS. 



The zone of gneiss just mentioned is, in the coast-chain 

 from the sea to the Villa de Cura, ten leagues broad. In 

 this great extent of land, gneiss and mica-slate are found 

 exclusively, and they constitute one formation.* Beyond 

 the town of Villa de Cura and the Cerro de Chacao the 

 aspect of the country presents greater geognostic variety. 

 There are still eight leagues of declivity from the table-land 

 of Cura to the entry of the Llanos ; and on the southern 

 slope of the mountains of the coast, four different forma- 

 tions of rock cover the gneiss. We shall first give the 

 description of the different strata, without grouping them 

 systematically. 



On the south of the Cerro de Chacao, between the ravine 

 of Tucutunemo and Piedras JSTegras, the gneiss is concealed 

 beneath a formation of serpentine, of which the composition 

 varies in the different superimposed strata. Sometimes it 

 is very pure, very homogeneous, of a dusky olive-green, and 

 of a conchoidal fracture : sometimes it is veined, mixed with 

 bluish steatite, of an unequal fracture, and containing 

 spangles of mica. In both these states I could not discover 

 in it either garnets, hornblende, or diallage. Advancing 

 farther to the south (and we always passed over this ground 

 in that direction) the green of the serpentine grows deeper, 

 and feldspar and hornblende are recognised in it: it is 

 difficult to determine whether it passes into diabasis or 

 alternates with it. There is, however, no doubt of its con- 



* This formation, which we shall call gneiss-mica-slate, is pecu- 

 liar to the chain of the coast of Caracas. Five formations must be dis- 

 tinguished, as MM. von Buch and Raumer have so ably demonstrated 

 in their excellent papers on Landeck and the Riesengebirge, namely, 

 granite, granite -gneiss, gneiss, gneiss -mica- slate, and mica-slate. Geo- 

 logists whose researches have been confined to a small tract of land, 

 having confounded these formations which nature has separated in several 

 countries in the most distiact manner, have admitted that the gneiss and 

 mica-slate alternate everywhere in superimposed beds, or furnish in- 

 sensible transitions from one rock to the other. These transitions and 

 alternating superpositions take place no doubt in formations of granite- 

 gneiss and gneiss-mica-slate ; but because these phenomena are observed 

 in one region, it does net follow that in other regions we may not find 

 very distinct circumscribed formations of granite, gneiss, and mica-slate. 

 The same considerations may be applied to the formations of serpentine, 

 which are sometimes isolated, and sometimes belong to the eurite, mica- 

 elate, and grunstelii. 



