the lowest, also, and have the most direct communication with those regions from which the mineral veins derive all their riches. 2. _Of Whinstone._ 61. Beside the veins filled with spar, and containing the metallic ores, the strata are intersected by veins of whinstone, porphyry, and granite, the characters of which are next to be examined. The term _whin_, or _whinstone_, with Dr. Hutton, like the word _trap_, with the German mineralogists, denotes a class of stones, comprehending several distinct species, or at least varieties. The common _basalt_, the _wacken_, _mullen_, and _crag_ of Kirwan, the _grûnstein_ of Werner, and the _amygdaloid_, are comprehended under the name of whin. All these stones have a tendency to a spathose structure, and discover at least the rudiments of crystallization. They are, at the same time, without any mark of stratification in their internal texture, as they are also, for the most part, in their outward configuration; and, as the different species here enumerated compose, not unfrequently, parts of the same continuous rock, the change from one to another being made through a series of insensible gradations, they may safely be regarded by the geologist as belonging to the same _genus_. 62. Whin, though not stratified, exists in two different ways, that is, either in veins, (called in Scotland _dykes_,) traversing the strata like the veins already described, or in irregular masses, incumbent on the strata, and sometimes interposed between them. In both these forms, whinstone has nearly the same characters, and bears, in all its varieties, a most striking resemblance to the lavas which have actually flowed from volcanoes on the surface of the earth. This resemblance is so great, that the two substances have been often mistaken for one another; and many rocks, which have been pronounced to be the remains of extinguished volcanoes, by mineralogists of no inconsiderable name, have been found, on closer examination, to be nothing else than masses or veins of whinstone. This latter stone is indeed only to be distinguished from the former, by a careful examination of the internal characters of both; and chiefly from this circumstance, that whinstone often contains calcareous spar and zeolite, whereas neither of these substances is found in such lavas, as are certainly known to have been thrown out by volcanic explosions. Now, from these circumstances of affinity between lava and whinstone, on the one hand, and of diversity on the other, as the formation of the one is known, it should seem that some probable conclusion may be drawn concerning the formation of the other. The affinity in question is constant and essential; the difference variable and accidental; and this naturally leads to suspect, that the two stones have the same origin; and that, as lava is certainly a production of fire, so probably is whinstone.