1864. ] Geology and Paleontology. . 121 
still retaining evidences of their former stratification. These instances 
might be greatly multiplied not only in the American States, but by 
numerous examples in Europe, and probably by some in our own islands. 
Indeed nowhere is there any evidence of the hypothetical granitic sub- 
stratum which, in even not yet very ancient treatises on Geology, we 
were taught to believe constituted the “ backbone of the earth.” Even 
one such example of interstratification would have gone far to throw a 
doubt upon the purely igneous origin of granite, but when instances 
become so multiplied the doctrine seems no longer tenable. Dr, Hitch- 
cock argues forcibly against it. The dry heat, he contends, that would 
be required to keep granite melted must be intense, for it resists the 
most powerful blast-furnaces, and even if, as melted matter, it were 
injected in close contact with the cold walls of fissured rock, it must 
have cooled before it had time to penetrate all the narrow crevices in 
which it is found in the form of veins. Again he urges that, if crys- 
tallized from such fusion, the quartz would have been consolidated and 
crystallized first, because it is less fusible than the mica and feldspar ; 
instead of which its condition in the structure of granite shows it to 
have been the last consolidated of the ingredients, for if anyone ex- 
amines a piece of granite, he will see the crystals of mica and feldspar 
are often perfect, while those of quartz are never so. The quartz is 
’ always in the amorphous state, and the sharp crystals of mica and feld- 
spar seem to cut into it, as is beautifully seen in graphic granite—an 
appearance which cannot be accounted for in any other way than that 
the mica and feldspar crystals were formed first, and that the quartz 
subsequently filled up the interstices. But such an admission is fatal to 
the doctrine of a cooling down from fusion by dry heat because, in that 
case, the quartz should have been, as we have said, the first to crystal- 
lize. Moreover, that granite contains not a few hydrated minerals, 
or such as contain water in their composition, is another fact telling 
also against the old opinions. 
In the matter of metamorphic rocks Mr. Sterry Hunt has also been 
continuing those valuable theoretical and practical researches of which 
he gave us two instalments in 1858 and 1859. Those articles were 
remarkable for the great ability of his attempts to indicate the ages 
of granites by the amounts of soda or potash they contained, and 
during the present year he has given to the world another elabo- 
rate paper, read before the Dublin Geological Society, on the chemical 
and mineralogical relations of the metamorphic, or, as they have been 
as commonly called, the crystalline primitive rocks. It is not indeed 
so very long since all rocks of this character were included in the com- 
mon designation of primitive, and were considered to belong to a 
period anterior to all the fossiliferous formations, and indeed to the 
existence of life, either vegetable or animal, on our earth. To express 
this idea, the term “ azoic”” was invented, while “ palzeozoic ” was given 
to the Silurian rocks, as containing the supposed first traces of ani- 
mated existence, or the “oldest life-forms,” on our planet. Some 
geologists still consider the Lower Silurian or Cambrian zone to be the 
first burial-ground of organic remains, and that no previous creation of 
animated beings or vegetation had taken place. Not only, however, 
