Page:Proceedings of the Royal Society of London Vol 1.djvu/173

Rh gradually propagate itself till the temperature of the glass is equal- ized, and then the recurrence of the circumstances which induced the ﬁrst particles to arrange themselves will cause other particles to arrange themselves also; and these the attraction of aggregation will dispose round the point ﬁrst formed. A second emission of heat every direction will now take place ; the temperature will again be equalized; and again another concentric coat of arranged particles will apply itself to the little globule. That these globules are formed of concentric coats does not clash with the circumstance of their being likewise radiated; as every one may have remarked the connexion that almost uniformly exists between the radiated structure and the formation by concentric coats; the more obvious instances of which are the hæmatites and the calcareous stalactites. In what manner this is likely to be effected is stated at some length in the paper.

Some curious remarks are next made on the observation of Mr. Smithson. that solution, far from being necessary to crystallization, effectually prevents its commencement; since, while solution sub- sists, crystallization cannot take place: and many of the phenomena being duly considered, it seems most probable that the particles of bodies apparently solid must be capable of some internal motion, enabling them to arrange themselves according to their crystalline polarity while they are in a solid state. Among the instances given, are the conversion of glass vessels into Reaumur's porcelain, the tem- pering of steel, and the process of annealing. This does not alto- gether disprove the crystallizations formed by molecules suspended in aqueous solutions; but it is in general insisted upon, that all cry- stallizations are dependent on heat, there being, in fact, no ﬂuidity, and consequently no solution, which heat does not produce.

These observations tend to prove the analogy which exists between the igneous and aqueous formations, and to show that precisely the same order and kind of arrangement is followed in the generation of stony masses from water as from ﬁre. Among the many instances that are adduced to justify this assertion, are, on the one hand, the phenomena exhibited by lavas, in which may be observed every step of the passage from the vitreous to the stony, from that to a porphy- ritic, and ﬁnally to the granitic state : on the other hand, we may select the formation of calcareous stalactites, in which the successive depositions of calcareous carbonate form a mass which at ﬁrst is ﬁbrous; a continuance of the process causes the ﬁbrous structure to disappear, and the stalactite becomes irregularly spathose ; after which the irregularities vanish altogether, and it becomes perfect calcareous spar, divisible into large rhomboids, with the form pecu- liar to that mineral.

Adverting now to the chief object of this paper,—the basalt,—-the author observes, that should, in fact, the analogy between the aqueous and igneous formation appear founded, the transition from glass to stone can no way affect the great question which has so long divided geologists about the origin of basalt: for though it be synthetically demonstrated that basalt may be formed by ﬁre, the proofs in favour