196 THE WONDERS OF GEOLOGY. Lect. III. 



of crystallized carbonate of lime, each crystal being com- 

 posed of millions of atoms of the same compound substances, 

 and having one invariable primary form — that of a rhom- 

 boid. Mechanical division is incapable of altering this 

 arrangement ; break the fragments as we may, we can 

 only separate them into a rhomboidal figure ; nor can this 

 condition be altered except by chemical decomposition. If 

 we pursue the investigation we find by analysis, that every 

 atom of these crystals consists of lime and carbonic acid, 

 each of which is made up of innumerable molecules. "Lime 

 and carbonic acid are also themselves compounds, lime con- 

 sisting of a metal called calcium and oxygen ; and carbonic 

 acid, of carbon and oxygen. Thus these ultimate particles 

 of calcium, carbon, and oxygen, form the indivisible atoms 

 into which all the secondary crystals of lime may be 

 reduced." * 



4. Stratification. — Having previously shown that the 

 disintegration and solution of the most refractory, and 

 apparently indestructible substances, may take place from 

 the conjoined effects of mechanical and chemical agency, 

 we proceed to the consideration of the manner in which 

 the debris of the ancient lands, and the accumulations in 

 the seas, have been converted into the rocks and strata that 

 form the existing islands and continents. The formation of 

 beach and sand, and the deposition of mud and clay in 

 layers or strata, and the subsequent consolidation of these 

 materials into rocks, have already been explained. And 

 here let me remind you, that strata are successive layers of 

 detritus spread over each other in such manner, as to allow 

 of the partial consolidation of one bed, before the deposition 

 of another upon it ; and a rock is said to be stratified, 

 when it presents the appearance of such divisions. Chalk 

 cliffs, and sandstone and limestone quarries, afford illus- 



* Dr. Buckland's Bridgwater E 



