M. de Carosi describes very systematically the generation of silex,
calcedony, onyx, and quartz, in calcareous earth, marl, gypsum,
sand-stone, and also what he terms _terre glaise, ou de l'Argile_. It is
in this last that we find a perfect analogy with what is so frequent in
this country of Scotland. These are the agates, calcedonies, calcareous
and zeolite nodules, which are found produced in our whin-stone
or subterraneous lavas, that is, the amygdaloides of Crondstedt.
Naturalists explain the formation of those nodular bodies differently.
The Chevalier de Dolomieu supposes these rocks to have been erupted
lavas, originally containing cavities; and that these cavities in the
solid rock had been afterwards filled and crystallised, by means of
infiltration, with the different substances which are found variously
concreted and crystallised within the solid rocks. Our author, on the
contrary, supposes these formed by a species of chemical transmutation
of calcareous and argillaceous earths, which, if not altogether
incomprehensible, is at least not in any degree, so far as I know, a
thing to be understood.
Pages:
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490