SCIENTIFIC SUMMARY. 
273 
that in that district at least, Plutonic masses do not perform the office of 
axes in elevations. The general idea is that the granitic rocks pushing 
up from below have bent up the over-lying stratified beds like the thatch 
on a hayrick ; but this view received a rude shock some time since, when 
Mr. Selwyn discovered, in Victoria, granitic masses which pierce old strata 
without affecting their dip, the dip on one side being coincident with that 
on the other side. And now, in Sutherland and Banffshire, Mr. Harkness 
believes the facts to indicate, that the water-formed deposits were upheaved, 
flexured, and contorted, prior to the period when granites made their 
appearance in them. And, finally, he tells us in so many words that, as 
regards its origin, there are “ abundant features which would support the 
conclusion that granite is, in that district, rather the result of an excessive 
amount of metamorphic action than a Plutonic rock.” What these 
“ abundant features” are, it would have been interesting to have learnt; 
but one that could not have been undervalued is the existence of the meta- 
morphic rock gneiss. Knowing as everyone does that that seeming granitic 
substance is really an altered sedimentary deposit, it only needs the hint 
to comprehend that the difference between granite and gneiss is one of 
degree and not of kind ; that these differ much less from each other than 
does gneiss from a water-formed rock ; and, therefore, when all the pre- 
ceding facts are remembered, it requires no stretch of the faith to lead to 
the conclusion that similar forces to those which produce metamorphic 
strata, only operating through longer periods or in greater intensity, may 
have formed granite. This would account for the correspondence of strilce, 
the coincidence of dip, the presence of water-globules, and many another 
otherwise unaccountable circumstance ; while it makes no demand on the 
assistance of deep-seated central forces. It is nowise our function to follow 
this thesis further, but the reader will probably see that if satisfactorily 
demonstrated, it will necessitate a new theory of the elevation and depres- 
sion of land. 
The origin of river valleys has long been a moot point. With that 
pertinacity which always characterizes scientific wars, one school has 
maintained that rivers erode their own channels, while the other party, 
triumphantly pointing to instances where streams go out of their way to 
pass through mountains, has held that they found the general features of 
their courses ready formed. In this state of our knowledge, or rather 
ignorance, Mr. Jukes comes forward to solve the riddle. His explanation 
is extremely startling, but probably in its general features true. Before 
giving an analysis, however, it will be but fair to say that, in our judg- 
ment, the new doctrine is not yet fully proved ; and that the essay in 
question, though philosophically conceived, and written with clearness, 
errs in sometimes regarding complex and debateable theories as axioms. 
The district selected for typical illustration is the South of Ireland, the 
central plain of which is carboniferous limestone, some 300 feet high. 
And to the south of it are several ranges of hills, some made of the 
subjacent old red sandstone and Cambro-Silurian, others of the super- 
imposed Coal rocks, and it is from these that the streams to be mentioned 
rise. 
In the case of every river examined, including the Shannon, Blackwater, 
