192 Proceedings of the Royal 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 much 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 be^^ond 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 
