208 
POPULAE SCIENCE EEYIEW. 
Analysis of Greenstone Dyhe^ Penrliyn Quarries. 
Water of Combination 1-99 
Bisulpbide of Iron 0*23 
Protoxide of Iron 10-22 
Peroxide of Iron 1-97 
Titanic Acid 2*51 
Alumina 5-80 
Sulphate of Lime 0-08 
^Carbonate of Lime 14-85 
^Carbonate of Magnesia 14*59 
Potash 0*43 
Soda 0*70 
Silica 47*47 
100*633 
Chemical Geology in the Formation of the Earth. — In chemical geology, 
the discussion between Dr. Sterry Hunt and Mr. D. Porbes is doing good, 
by directing attention to this interesting branch of the science. Some of 
the questions at issue are necessarily so theoretical as not to admit of direct 
proof, and consequently allow of great latitude of opinion. Thus whilst 
Dr. Hunt insists upon the earth being solid to the core ; that its surface 
immediately before complete solidification was covered by a shallow sea of 
molten matter, surrounded by an intensely acid atmosphere, containing hy- 
drochloric and sulphurous acids ; and that the saltness of the sea was due to 
the action of a rain of hydrochloric acid deluging the half-cooled crust — Mr. 
Forbes contends that the surface of the globe was not the last to solidify; 
that it still contains some reservoir of fluid igneous matter, from which 
volcanic lavas proceed ; that the primeval atmosphere differed mainly from 
the present in containing much less oxygen along with a great excess of car- 
bonic acid and steam ; and that the sea was salt from the beginning owing 
to the water when condensed on to the earth dissolving the salt and other 
chlorides, &c., in its external crust. In this discussion, however, other 
problems of great importance, and capable of being ultimately solved by 
experimental and field observations are considered, as for example, amongst 
others, whilst Dr. Hunt, in all cases, regards granite as a sedimentary rock, 
and quartz as an aqueous product, Mr. Forbes shows that analogous rocks 
containing quartz are lavas from active volcanoes, and consequently in such 
cases must be igneous. He disputes Dr. Hunt’s theories of the origin of 
limestone, dolomite, and gypsum, contending that most limestones are 
formed by organic life assimilating the compounds of lime in the sea, and 
not precipitates thrown down by carbonate of soda, and points out that all 
the magnesian limestones and gypsum beds could not, as Dr. Hunt advances, 
have been formed in a dense atmosphere of carbonic acid, since the greatest 
development of such strata occurred at a period when animals existed upon 
the face of the globe, which could not have lived in such an atmosphere. 
♦ — 
* The carbonate of lime (and magnesia ?) occurs for the greater part in 
the shape of separate crystals, which are visible in a fresh fracture to the 
naked eye, and effervesce in isolated spots on the application of hydrochloric 
acid. 
