earthy, ochraceous substance. This earthy matter is of a pale yellowish-
brown colour, and appears to be a mixture of carbonate of lime with iron;
it effervesces with acids, is infusible, but blackens under the blowpipe,
and becomes magnetic. The rounded form of the minute patches of earthy
substance, and the steps in the progress of their perfect formation, which
can be followed in a suit of specimens, clearly show that they are due
either to some power of aggregation in the earthy particles amongst
themselves, or more probably to a strong attraction between the atoms of
the carbonate of line, and consequently to the segregation of the earthy
extraneous matter. I was much interested by this fact, because I have often
seen quartz rocks (for instance, in the Falkland Islands, and in the lower
Silurian strata of the Stiper-stones in Shropshire), mottled in a precisely
analogous manner, with little spots of a white, earthy substance (earthy
feldspar?); and these rocks, there was good reason to suppose, had
undergone the action of heat,--a view which thus receives confirmation.
This spotted structure may possibly afford some indication in
distinguishing those formations of quartz, which owe their present
structure to igneous action, from those produced by the agency of water
alone; a source of doubt, which I should think from my own experience, that
most geologists, when examining arenaceo-quartzose districts must have
experienced.

The lowest and most scoriaceous part of the lava, in rolling over the
sedimentary deposit at the bottom of the sea, has caught up large
quantities of calcareous matter, which now forms a snow-white, highly
crystalline basis to a breccia, including small pieces of black, glossy
scoriae. A little above this, where the lime is less abundant, and the lava
more compact, numerous little balls, composed of spicula of calcareous
spar, radiating from common centres, occupy the interstices. In one part of
Quail Island, the lime has thus been crystallised by the heat of the