DIALLAGE ROCK. 195 



direction and the dip of the heds being easily traced, 

 and their dimensions also admitting of measurement. 

 At Fedaland point too, where thin beds of this rock 

 are interposed among other primary schists, the regu- 

 larly stratified disposition is obvious. 



Like many more of the primary strata, Diallage rock 

 presents a considerable variety of connexion ; being 

 found in contact with gneiss, with micaceous, chlorite, 

 and argillaceous schists, and with serpentine. It also 

 alternates with every one of these rocks ; while the 

 large masses contain thin beds of these substances, and 

 of hornblende, talcose, and actinolite s'chists, with, more 

 rarely, serpentine. It further appears to pass into tal- 

 cose and chlorite schists ; and in those cases, the essen- 

 tial mineral, diallage, appears to change its character 

 so as to graduate into talc, or chlorite : felspar remain- 

 ing. The apparent passage into serpentine occurs 

 where the diallage rock approximates to that substance. 

 In this case, the felspar seems to be excluded, and a 

 serpentine substituted in its place ; though from the 

 dark colour of the compact felspar in this compound, 

 and the hard nature of the serpentine, they are 

 scarcely distinguishable in the state of minute admix- 

 ture with diallage. 



In concluding this account of its geological con- 

 nexions, I must observe, that all reports seem to note 

 its frequent or peculiar connexion with serpentine^ 

 though it is not easy to conjecture what necessary af- 

 finity should exist between them. This appears to be 

 the fact on the continent of Europe, as it is in Corn- 

 wall and in Shetland ; in these islands, even the small- 

 est masses of it are accompanied by portions, equally 

 insignificant, of Serpentine. 



In this imperfect state must the history of Diallage 

 rock remain, till foreign geologists shall furnish us with 



o 2 



