150 DOMAIN II. SILICEOUS. 



a great quantity; and Stonehenge is built of these 

 blocks. So blocks of granite are found in Bran- 

 denburg, Mecklenburg, and Pomerania*. 



Mountains of granular quartz abound in Scot- 

 land ; and granitic mountains in Sweden. When 

 the continents were gradually emerging, and before 

 these large subsidences which form mediterranean 

 seas, it may easily be conceived that the plains 

 where such blocks, and gravel foreign to the sur- 

 rounding mountains, are always found, were co- 

 vered for ages by the waters of the ocean, which 

 rolled these blocks and gravel in the direction of 

 their currents. 



In a late volume of the Philosophical Trans- 

 actions f, Bournon gives some observations on the 

 different modes of attraction, which influence the 

 formation of minerals. The attractions of aggre- 

 gation are either simple or crystalline. 



" It sometimes happens (owing perhaps to a 

 more considerable degree of disturbance during 

 the process of attraction), that there are found 

 small irregular detached masses, often so minute 

 as to be scarcely perceptible ; at other times they 

 are of a larger size, and, as soon as formed, fall to 

 the bottom of the liquor, and unite together by a 



* De Luc, Geologic. Paris 1809, 8vo. p. 332. 

 f 1804, p. 37. 



