192 Proceedings of the Boyal Physical Society. 



with other fossiliferous strata, or contain, in some of their 

 less metamorphosed beds, remains whose age can be deter- 

 mined, there can be no error and mach advantage in calling 

 them by the name of the system to which they belong, and 

 discarding the term metamorphic. But where all sequential 

 connection is lost, or at all events obscure and uncertain, 

 and where not a trace of organism has been detected, as in 

 the schists of our Scottish Highlands, it seems to be safer 

 and more philosophical to regard- them as simply " meta- 

 morphic," rather than designate them by the name of any 

 system — Silurian or Cambrian — to either of which, to both 

 of which, or to none of which they may yet be discovered 

 to belong. The geological map of Europe is made more in- 

 telligible by marking the metamorphic strata of the Alps 

 (for example) by the colour of the system to which they 

 belong, but it is more than questionable how far the geology 

 of Scotland is explicated, or the science itself promoted, by 

 delineating, as has been recently attempted, the crystalline 

 schists and quartzites of the Highlands as lower Silurian. 

 As a fact, the term metamorphic conveyed no error ; as a 

 hypothesis the designation Silurian, in absence of all fossil 

 evidence, imparts no new knowledge, and tends to retard 

 investigation. In the second place, some geologists are evi- 

 dently carrying the idea of metamorphism beyond its legiti- 

 mate limits, and would ascribe to its in tenser manifestations 

 the production of the granites and granitic compounds. 

 Now, no one who has studied the porphyritic gneisses of our 

 own Highlands will deny that some granites may be the 

 result of intense metamorphism ; but to assume that all 

 granites have had this origin, and that none of them are 

 truly eruptive rocks, is, in my opinion, an obvious error. 

 Carry, if you will, with Sir William Logan, metamorphic 

 action to such intensity as to render the masses plastic or 

 semifluid, and what then ? Simply this, that you have a 

 highly heated or vulcanic product capable of being forced 

 into rents and fissures, and to all intents intrusive. But 

 does it never occur to those who would deny the eruptive 

 character of some granites, that these granites, like the 

 schists with which they are associated, have undergone a 



