397 



FOREIGN COEEESPOKDEKCE. 

 By Dk. T. L. PfliPsoN, OE Paris. 

 Formation of Prairicc and, their relation to Peat-logs. 



(Continued from page 248.) 



The distinguished botanist, M. Alphonse De Candolle, has remarked, 

 that these ideas of ]M. Lesquereux are undoubtedly true as regards a 

 great number of prairies, but they cannot be applied, he thinks, to 

 every country, nor can he admit that they arc applicable to all the 

 prairies of North America. M. Desor, who has also visited the United 

 States, and who was present at the reading of M. Lesquereux's paper, 

 says he cannot attribute to the above causes the formation of what are 

 termed frairies roulantes, or undulating prairies, which are very 

 frequent in North America. We might also object that in hot 

 countries — for instance, in Louisiana, on the banks of the river 

 Amazon, of the Oronocco, of the Ganges, &.c, — we have examples of 

 ligneous vegetation in the shape of trees belonging to the families of the 

 Anonacecd, Rhizoplioracecd, and even Papilionaceoi and Avicennece, which 

 transform the marshy banks of these rivers into jungles — often into 

 magnificent forests. 



ITew observations on Silica — Its radical Siliciain compared ivitli Carlon 

 and Boron — Composition of Carbonic, Boric, and Silicic Acids — The 

 Archegosaurus — Sand-banJcs of the Pacific Ocean — Effects of Earth" 

 qualics upon Ayiimals. 



Silicic acid is found in nature in the form of sand, sandstone, silica, 

 flint, quartz, amethyst, agate, opal, jaspar, silicified wood, &c. Com- 

 bining with the different oxides, it forms salts called Silicates. Thus 

 the emerald is a silicate of alumina and glucina ; garnet, a silicate of 

 alumina and iron ; calamine, a silicate of zinc ; clay, a silicate of 

 alumina ; talc, a silicate of magnesia, &c. 



Silicic acid is, therefore, one of the most abundant of mineral substances, 

 and, at the same time, one of the most universally diffused, Koene says 

 it is the most abundant of all bodies," and that it forms two-thirds 

 of the earth's crust ;" and this figure is far from exaggerated. The 

 true nature of silicic acid, however, only began to be investigated about 

 the year 1807, and its composition was not rendered evident until a few 

 years later, when Berzelius extracted from it silicium, a simple element, 

 which, on combining with a certain quantity of oxygen, produces the 

 white powder known as silicic acid. 



Up to the present time, the nature and properties of both silicium 

 and its acid have been very incompletely known. We are told in books 

 that silicic acid is composed of one atom of silicium and three atoms of 

 oxygen j that silicium is a brown powder, and that its atomic weight is 



2 A 



