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ESSAY VI.

ON THE PROPERTIES OF ROCKS, AS CON-NECTED WITH THEIR RESPECTIVE AGES.

I. ON THE INGREDIENTS OF ROCKS.

It was a favourite idea some time since,that the simple earths a were older than thecompound.

It was supposed, also, that siliceous brocks were older than calcareous. M. Le-febre c and M. Dolomieu took great pains in1791, to establish the then-disputed exist-ence of primitive lime-stone.

These doctrines it is unnecessary to dis-

* Journal de Physique, vol. xxxix. p. 374.b L’Encyl. Geographic Physique, vol. i. p. 96.e Journal de Physique, vol. xxxix.