Limestones Organic. 17 



formed entirely by the life and death of animals that 

 lived in water. In many a formation for instance, in 

 some of the masses great and small of the Carboniferous 

 Limestone the eye tells us that they are formed 

 perhaps entirely of rings of encrinites or stone-lilies, or 

 of shells and corals, of various kinds, or of all these 

 mixed together ; and in many other cases where the 

 limestone is homogeneous, the microscope reveals that 

 it is made of foraminifera, or of exceedingly small 

 particles of other organic remains. Even when these 

 fragments are indistinguishable to the naked eye, 

 reflection tells us that such marine limestone deposits 

 must have been built up from the debris of life, for 

 there is no reason to believe that vast formations of 

 limestone, extending over hundreds of square miles, 

 are now, or ever have been precipitated in the open 

 ocean by inorganic chemical processes acting on mere 

 chemical solutions. It sometimes happens, indeed, that 

 gradual accumulations of such beds of limestone have 

 attained thousands of feet of vertical thickness in what 

 belongs to recent times in a geological sense, as for 

 example in the great coral reefs of the Pacific Ocean, 

 and, in less known degree, in the calcareous and fora- 

 miniferous mud of that ocean and of the Atlantic. 



But where does the carbonate of lime come from by 

 which these animals make their skeletons? If we 

 analyse the waters of springs and rivers, we discover 

 that many of them consist of water that is more or less 

 hard that is to say, not pure, like rain-water, but 

 containing various salts in a state of chemical solution, 

 the most important of which is generally bicarbonate 

 of lime ; for the rain-water that falls upon the land 

 percolates the rocks, and, rising again in springs, carries 

 with it salts of soda, potash, &c., and, if the rocks be 



c 



