GEOLOGICAL CONCLUSIOA'S. 309 



afforded no certain proof of any connection between the fires 

 of the mountain and the formation of the chalk. 



The fine earthy texture of the material is evidence that the 

 deposit was not a siibaerial seashore accumulation, since only 

 sandstones and conglomerates, with rare instances of more 

 compact rocks, are thus formed. Sand-rock-making is the 

 peculiar prerogative, the world over, of shores exposed to waves, 

 or strong currents, either of marine or fresh water. We 

 should infer, therefore, that the accumulation was produced 

 either in a confined area, into which the fine material from a 

 beach may have been washed, or on the shore of a shallow, 

 quiet sea ; in other words, under the same conditions nearly 

 as are required to produce the calcareous mud of the coral 

 island. But, although the agency of fire in the result cannot 

 be proved, it is by no means improbable, from the position 

 of the bed of chalk, that there may have been a hot spring 

 at the spot occupied by it. That there \vere some peculiar 

 circumstances distinguishing this from other parts of the reefs 

 is evident. 



This, if a true conclusion, is to be taken, however, only as 

 one method by which chalk may be made. For there is no 

 reason to suppose that the chalk of the Chalk-formation has 

 been subjected to heat. On the contrary, it is now well ascer- 

 tained that it is of cold-water origin, even to its flints, and that 

 it is made up largely of minute forammifers, the shells of 

 Rhizopods. Professor Bailey found under his microscope no 

 traces of foraminifers, or of anything distinctly organic, in the 

 Oahu chalk. 



XI. RATE OF INCREASE OF LIMESTONE FORMATIONS. 



On page 212 it is shown that coral-reef limestones are of 

 slow formation, the rate of increase in thickness, where all is 

 most favourable, not exceeding perhaps a sixteenth of an inch 

 a year, or five feet in a thousand years. And yet such lime- 

 stones probably form at a more rapid rate than those made of 

 shells, because the animals are to a larger extent calcareous, or 



