282 Prefuce to “ The Natural History 
Iron is blended in great quantity in the composition of most 
of our rocks, and so abundantly in some of them, as to be worth 
smelting out for use; and, moreover, we have in many places 
great numbers of whole strata of iron-stone so rich as to be equal, 
if not to exceed, the best of our iron ores in the produce of the 
furnace. 
In working downwards, many of our mineral veins are eut out, 
and fail at various depths, by a different stratum coming in ber 
low, which the vein does not penetrate. The rich vein of lead 
at Llangunog, in Montgomeryshire, which was five yards wide of 
solid ore, was cut off below in this manner: 
A bed of schistus. came in at a certain depth below, which cut 
out both the ore and the vein so entirely, that no vestige of 
either entered the schistus, or could ever after be found. Ex- 
tensive trials were made on all hands to no purpose, as neither 
vein nor ore ever appeared. 
These circumstances do not agree with the idea of our ores 
being formed by mineral steams, forced up by subterraneous 
fires; and therefore we must acknowledge, that the substances 
of which our ores have been formed were poured into our veins 
by water from above, as well as the various spars and all the 
contents of mineral veins. 
‘There is a curious and surprising mixture of many different 
substances in several mineral veins. In some of them, we find 
lead, copper, silver, and several other metallic and semi-metallic 
ores; and, in the same vein, we find calcareous and siliceous 
spar, with a variety of other stones and mineral matters of various 
colours, qualities, and degrees of hardness; and we frequently 
find many of these, and sometimes all of them, blended together 
in the concavity of the same vein. 
Every phenomenon of these different ores and different stones 
proves to ocular demonstration, that all the different substances 
in the composition were poured in from above, and mixed to- 
gether while in a humid or fluid state, and that they were after- 
wards consolidated together into such compound masses as we 
find them. 
IV. The fourth proposition offered to our consideration, in 
our author’s Theory of the Earth, is also pretty singular, which 
is, that these operations of nature, viz. the decay and waste of 
the old land, the forming and consolidation of new land under 
the waters of the ocean, and the change of the strata now form- 
ing under water into future dry land, is a progressive work of 
nature, which always did, and always will go on, forming world 
after world in perpetual succession. 
This hypothesis agrees pretty nearly with Count Buffon’s, 
only that the Count brings about his successive changes hy a 
watery 
ve 
