370 ET3ATA OF THE SIERBA PA RIMS. 



tion, we would distinguish mineralogically between the rocks 

 of granite, gneiss, and mica-slate, it must be borne in mind 

 that coarse-grained granite, not passing to gneiss, is very rare 

 in this country. It belongs peculiarly to the mountains that 

 bound the basin of the lake of Valencia towards the north j 

 lor in the islands of that lake, in the mountains near the 

 Villa de Cura, and in the whole northern chain, between the 

 meridian of Vittoria and Cape Codera, gneiss predominates, 

 sometimes alternating with granite, or passing to mica-slate. 

 Mica-slate is the most frequent rock in the peninsula of 

 Araya and the group of Macanao, which forms the western 

 part of the island of Marguerita. On the west of Mani- 

 quarez, the mica-slate of the peninsula of Araya loses by 

 degrees its semi-metallic lustre ; it is charged with carbon, 

 and becomes a clay-slate (thonschiefer) even an ampelite 

 (alaunschiefer) . Beds of granular limestone are most com- 

 mon in the primitive northern chain; and it is somewhat 

 remarkable that they are found in gneiss, and not in mica- 

 slate. 



We find at the back of this granitic, or rather micaslate- 

 gneiss soil of the southern chain, on the south of the Villa de 

 Cura, a transition stratum, composed of greenstone, amphi- 

 bolic serpentine, micaceous limestone, and green and carbu- 

 retted slate. The most southern limit of this district is 

 marked by volcanic rocks. Between Parapara, Ortiz, and 

 the Cerro de Flores (lat. 9 28' 9 34' ; long. 70 270 

 15'), phonolites and amygdaloids are found on the very 

 border of the basin of the Llanos, that vast inland sea which 

 once filled the whole space between the Cordilleras of 

 Venezuela and Parime. According to the observations of 

 Major Long and Dr. James, trap-formations (bulleuses 

 dolerites and amygdaloids with pyroxene) also border the 

 plains or basin of the Mississippi, towards the west, at the 

 declivity of the Rocky Mountains. The ancient pyrogenic 

 rocks which I found near Parapara where they rise in mounds 

 with rounded summits, are the more remarkable as no others 

 have hitherto been discovered in the whole eastern part of 

 bouth America. The close connection observed in the strata 

 of Parapara, between greenstone, amphibolic serpentine, 

 and amygdaloids containing crystals of pyroxene ; the form 

 of I he Morroa of San Juan, which rise like cylinders above 



