ABSENCE OF KOCK8. 101 



which in these latter years has furnished a subject of specu- 

 lation to geologists, occupied us much during our journey 

 across the LlanDs. I allude not to those blocks of primitive 

 rock which occur, as in the Jura, on the slope of limestone 

 mountains, but to those enormous blocks of granite and 

 syenite, which, in limits very distinctly marked by nature, 

 are found scattered on the north of Holland, Germany, and 

 the countries of the Baltic. It seems to be now proved, that, 

 distributed as in radii, they came, at the time of the ancient 

 revolutions of our globe, from the Scandinavian peninsula 

 southward ; and that they did not primitively belong to the 

 granitic chains of the Harz and Erzgeberg, which they 

 approach, without, however, reaching their foot.* I was 

 surprised at not seeing one of these blocks in the Llanos of 

 Venezuela, though these immense plains are bounded on the 

 south by the Sierra Parima, a group of mountains entirely 

 granitic, and exhibiting in its denticulated and often columnar 

 peaks traces of the most violent destruction. Northward, the 

 granitic chain of the Silla de Caracas and Porto Cabello are 

 separated from the Llanos by a screen of mountains, that are 

 schistose between Villa de Cura and Parapara, and calcareous 

 between the Bergantin and Caripe. I was no less struck by 

 this absence of blocks on the banks of the Amazon. La 

 Condamine affirms that from the Pongo de Manseriche to the 

 Strait of Pauxis not the smallest stone is to be found. Now 

 the basin of the Eio Negro and of the Amazon is also n- 

 Llano, a plain like those of Venezuela and Buenos Ayres. 

 The difference consists only in the state of vegetation. The 

 two Llanos situated at the northern and southern extremities 

 of South America are covered with gramina ; they are tree- 

 less savannahs; but the intermediate Llano, that of the 

 Amazon, exposed to almost continual equatorial rains, is a 

 thick forest. I do not remember having heard that the 

 Pampas of Buenos Ay res, or the savannahs of the Missouri t 

 and New Mexico, contain granitic blocks. The absence of 

 tliis phenomenon appears general in the New "World, as it 

 probably also is in Sahara, in Africa ; for we must not con- 

 found the rocky masses that pierce the soil in the midst of 



* Leopold von Buch, Voyage en Norwege, vol. i. p. 30. 



t Are there anj isolated block* in North America northward of tha 



