SERPENTINE. 203 



formed from some argillo-arenaceous stratum, in the 

 manner hereafter indicated in treating of that rock. 



This view is now confirmed by facts occurring near 

 Borghetto, at Monte ferrato, near Prato in Tuscany, 

 and elsewhere ; the defect of Brongniart's observations 

 being corrected by others, who have shown that these 

 overlying masses are partial, and are connected with 

 deep-seated ones beneath, filling great rents in the pri- 

 mary strata, while the diallage rock, of various aspects, 

 often includes masses of serpentine, together with those 

 botryoidal siliceous schists so frequent in the vicinity 

 of trap. There can therefore remain no doubt that 

 there are veins of serpentine, and that both serpentine 

 and diallage rock thus bear the analogy to trap which 

 I have here suggested. And the confirmation is ren- 

 dered complete, by the further remark, that the 

 neighbouring schists have been indurated, that the 

 sandy marls have become jaspideous substances, as in 

 the junction with trap and granite, and that both the 

 diallage rock and serpentine are found in the form of 

 veins and of nodules, mutually imbedded or traversing. 



With all these facts, (and more do not seem neces- 

 sary,) the theory of Serpentine now becomes suffici- 

 ently easy ; it being explained how it is stratified, un- 

 stratified, and venous, and how it occurs in both classes. 

 There is no instance where a rock stratified from 

 water, however subsequently changed by heat, forms 

 veins, as, in fact, it could not, from the very nature of 

 a vein. Serpentine is not, therefore, in every case, an 

 aquatic stratum, nor can it be, in every one, a fluid 

 intruding rock, like trap and granite. It is both ; 

 thus leaving to geologists the choice of its place, as I 

 already said* When truly stratified, not in pseudo- 

 strata, as in Brongniart's case, it must be compared with 

 gneiss, as an aquatic stratum changed by heat, finding 



