397 
POKEIGN COERESPONDENCE. 
Br De. T. L. PmpsoN, of Paeis. 
Formation of Prairies and their relation to Peat-logs. 
(Continued f rom page 248.) 
The distinguished botanist, ]M. Alphonse De Candolle, has remarked, 
that these ideas of M. Lcsquureux 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 are 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 2^rairies 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, Rhizophoracea:, and even Papilionacece and Aviccnnece, which 
transform the marshy banks of these rivers into jungles — often, into 
magnificent forests. 
New observations on Silica — Its radical Silicium compared tvith Carhon 
and Boron — Comj>ontion of Carbonic, Boric, and Silicic Acids — The 
Archegosaurus — Sa)id-hanlcs of the Pacific Ocean — Effects of Earth' 
quakes upon Animals. 
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. Kcene 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 ; that silicium is a brown powder, and that its atomic weight is 
2 A 
