96 Dr. B E R G E R on the physical Structure 



This cause has operated not only on flints, but also on every kind of 

 rock, forming detached masses or entire mountains, which have been 

 worn down either in whole or in part, and the fragments afterwards 

 transported, and deposited in the plains by currents of water.* It is 

 principally the same agent which has accumulated the heaps of quartz 

 pebbles, which are found at the extremities of some primitive 

 countries,t on elevated plains, to the nature of which they are quite 

 foreign : it is however much more difficult to trace with any cer- 

 tainty the original locality of this quartz, than of flint gravel.:|: 



With regard to the formation of flints in chalk, if we adopt the 

 explanation of Werner, that they have been produced by infiltration, 

 I should be as much disposed to attribute the void spaces in the chalk 

 to a natural contraction of its own substance, as to the disengagement 

 of air. We know that chalk divides by drying, into compartments 

 which are sometimes very regular, nearly in the same way as marl. 

 According to this hypothesis we may suppose, either that the chalk 

 and the flints are of contemporaneous formation, that the elements of 

 the flint were mixed with those of the chalk, and that they separated 

 from each other by elective affinity, or that the siliceous matter has 

 been afterwards introduced, and has iilled up the cavities left in the 

 chalk. 



But whichever of these opinions we may adopt, I do not see, how 

 in any case we can possibly admit the conversion of chalk into flint, 



* Saiissure, Voyages aux Alpcs, ^^. 1313. 1327, 13^9. 1331. 



+ For example, at the entrance of the great valley of the Rhone, in the neighbourhood 

 of Lyons. 



J Sir Henry Englcfield has pointed out in the Isle of Wight, a very remarkable fact 

 relative to the state of the flints imbedded in the chalk. Transact, of tlie Linnaian Soc. 

 jTol. vi. p. 103 and 303. See also for a fact nearly similar to the preceding, Geographic 

 Physique de Bergman. Jouru. des Mines, No. xvi. p. 39. 



