Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/108

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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, on elevated plains, to the nature of which they are quite foreign: it is however much more difficult to trace with any certainty 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 filled 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,