120 Chronicles of Science. [Jan 
a quarterly summary of the nature of the present article, there must 
necessarily therefore be, as a rule, less definiteness and more hesitation 
and uncertainty than one would wish, but notwithstanding this in- 
herent difficulty in the task, it is perfectly possible to give a concise 
and clear account of what is new and what is changing; but it must be 
more or less the newness of theories as well as of facts, bearing always 
in mind that geological facts are first provisionally accepted on the 
reliability of the observer, and are often open not only to questioning 
but to reversal, Thus for many years the older crystalline or meta- 
morphic rocks were regarded as owing their characteristic structure 
to their contact with other heated or so-called igneous rocks,—such as 
granite was supposed originally to have been, constituting the lower 
zone at least of the crust -of the planet we inhabit. 
For some time past, some of our most acute and practical geolo- 
gists have more than doubted the old doctrines, and our own Sorby, 
by detecting the existence of steam-bubble cavities in granite, decisively 
proved that dry heat had not been the cause of its crystalline change. 
Dr. Rubidge, who has done so much good geological work at the Cape 
of Good Hope, also years before threw doubts on the heat-origin of the 
changes exhibited by the metamorphic rocks, by stating the occur- 
rence, in the district of Port Elizabeth, of intercalated metamorphosed 
strata with unchanged sedimentary beds above and belowthem. Such 
examples have since been from time to time not unfrequently timidly 
recorded, but they are now being more boldly noticed. Dr. Hitchcock, 
very lately speaking of the granites of Maine, in the Northern States 
of America, regarded the old theory that granite was once melted 
matter thrust into every crack of the overlying strata as erroneous, 
and substitutes the aqueo-igneous explanation of a plasticity of the 
original materials by means of steam, the primal structure of the rock 
béing thus obliterated, and a new crystalline condition induced. He 
thinks that granite may thus have been formed out of schists, and these 
originally from shales and sandstones, and contends that it is ‘“‘ only 
an example of metamorphism carried to its utmost limit—carried far 
enough to obliterate all traces of stratification, foliation, and lamina- 
tion.” Observation, he further claims, shows that granite does not 
always constitute the axes of mountains, but that it lies between strata, 
and instead of having been the agent by which they have been lifted 
up, it has partaken of the general movements which have resulted from 
general causes. In York and Oxford counties, in Cumberland, and 
Franklin, he notices the intermixture of granite with bands of sedi- 
mentary strata, and constantly speaks of it as ‘‘ comporting itself like 
a stratified rock.” That of Buckfield is mostly in the form of large 
beds and veins, and at Woodstock mica-schist is seen lying beneath it. 
Again, in the south-eastern counties of Maine, granite at the south 
end of Bluehill Neck, overlies strata of gneiss and mica-schist ; and 
in the Kennebec region it is said that in one of the Hallowell quarries 
there are twenty-six different sheets, varying from eight inches to four 
feet in thickness, and that “ these sheets are arranged like strata.” In 
Canada, too, even the granites of the Lamentian and Lower Silurian 
age appear in every case to be indigenous strata altered in situ, and 
