Presidents Address. 
193 
raetamorphism of their own, and that they were originally 
truly igneous like the basalts and greenstones. Place, for 
example, the carboniferous and old red strata of Edinburgh, 
with their associated porphyries, basalts, and greenstones, at 
great depths in the crust, and subject them to metamorphic 
action, and what would be the likely result ? Evidently, that 
while the sandstones and shales and limestones and ironstones 
were being converted into crystalline schists and marbles 
and haematites, the porphyries and greenstones would also 
undergo metamorphism, and be changed into granites and 
syenites. So in all probability it has been with the old 
crystalline schists and their associated granites — both have 
undergone a metamorphism, but the former is not less sedi- 
mentary, nor the latter less eruptive or igneous, because of 
this internal mineral re-arrangement. Let us then clearly 
understand what we mean by the term metamorphic^ and 
take care how it is applied. It is a convenient term for 
altered strata whose age we cannot determine by the aid of 
fossil organisms. It is a sound designation when applied 
to altered rocks, whether sedimentary or igneous ; but its 
action, however intense, does not affect the fact that such 
rocks were primarily of aqueous and igneous origin. Some 
granitic masses maybe merely highly metamorphosed schists, 
but that does not affect the circumstance that others are 
truly igneous, though altered in their mineral texture by a 
similar metamorphism. The truth is, every substance in 
the earth's crust is continuously and incessantly undergoing 
metamorphism — the latest eruption of lava, as well as the 
latest deposition of sea-silt, or the vegetable layer which 
last summer's growth contributed to the gradually increas- 
ing peat-bog. Heat by contact, heat by transmission, con- 
duction, or absorption, heat by permeation of hot water, 
electric and magnetic currents, chemical action and reaction, 
molecular re-arrangement under pressure, and the like, are 
all conducing to this mineral change ; but though we fail to 
detect in every instance the producing causes, we need not 
on that account, and for the sake of some cherished hypo- 
thesis, confound the obvious results. 
Passage Beds, — Another point of our science which re- 
