VOL. LXXXI.] PHILOSOPHICAL TRANSACTIONS. Q 



sition, and doubtless also in origin, and to the hornstein of the Germans; a 

 term including petrosilex and several sorts of close grained vvhinstone, of which 

 there are found in England varieties with a conchoidal fracture, semi-transparent 

 at the edges, and in other respects fast approaching to a siliceous nature. Lille- 

 shall Hill near Shifnal, in Shropshire, to mention a single instance, affords such 

 siliceous, besides semi-granitic, porphyritic, and common vvhinstone, containing 

 agate. 



But basaltes, of which a right knowledge is conducting us fast to a just theory 

 of the earth, is not less connected with granite; insomuch that we may trace 

 those rocks gradually approaching and changing into one another. Dr. B. has 

 had an opportunity of examining many connecting links in this gradual suc- 

 cession; and this opinion, which has since been confirmed by other considera- 

 tions, was first forced on him by specimens in great variety from volcanic and 

 basaltic countries. But as it is a point by far too important to be admitted on the 

 mere authority of any mineralogist, he endeavours to support it by the testimony 

 of observers, who cannot be suspected of any bias towards such an hypothesis. 

 The first step in the progression appears at the Giant's Causeway in Ireland. 

 Many of the pillars there consist of fine-grained, dark-coloured whinstone; that 

 variety which may be considered as most perfect, and as equidistant from por- 

 phyry, petrosilex, and granite; but at the promontory of Fairhead, the character 

 of the stone is seen to alter, and it has lately been described as an imperfect kind 

 of granite. Hence we are led by regular approaches to perfect prisms of granite, 

 accompanied by prisms of common whinstone, and not less obviously than the 

 different ranges on the coast of Antrim betraying a common origin. The pillars 

 of Lex Rameux, though they rather incline towards the dark colour and uniform 

 hard substance; " yet, when broken, are unequal both in colour and texture, 

 and sometimes interspersed with irregular pieces and patches, as it were, of an 

 heterogeneous hard substance, which by its micse and small rhomboidal crystal- 

 lizations, much resembles a sort of granite frequently seen. The mass on which 

 these columns stand is of the same mixed character." Other examples will 

 occur afterwards ; and for basaltiform colonnades of granite, it is only necessary 

 to refer to Mr. Strange's description of Monte Rosso. The general shape of 

 the Euganean hills, as if suddenly raised by the expansive and effervescent force 

 of heat from the surrounding plain, the lava intermixed with granite, as if both 

 had concreted together, the columns of a uniform texture in the adjacent parts 

 of these hills, and the .rest of the phenomena, even then led the author to 

 suspect, " a strong analogy between granites and many particular volcanic con- 

 cretions." 



From the mountain of Esterelles, in the south of France, on the road from 

 Frejus to Antibes, Dr. B. had granite, gneiss, and specimens, in which felds- 



VOL. XVII. C 



