TIIK MEDITERRANEAN NAT UK A LIST 
65 
schistose by pressure, or are partly granitic intrus- 
ions, it is evident to anyone practically familia. 
with dynamical principles that they have been 
subjected to enormous pressure deep down in the 
earth, and have been thereby forced up, behaving 
under such pressure in most respects like plastic 
bodies. 
It will be seen from this only too short descript- 
ion that the characteristics of great mountain 
ranges are in the regions of the ranges, great fold- 
ings of the strata, semi-plastic intrusions forming 
the central, or what formerly was the central core 
of the range, often enclosing the sedimentary folds 
in a manner expressively likened to “button-holes,” 
and frequently, in addition, intrusions of true gra- 
nite, and trappean or igneous dyke-rocks. These 
folds are, excepting in the case of those buried in 
the earth, truncated by erosion and atmospheric 
influences, so that even in geologically recent 
ranges as much rock has apparently been removed 
as that which remains above the general surface 
level; while, in the case of older chains, such as the 
Urals and the Appalachians, the remaining port- 
ions are mere worn down stumps. This is the case 
with our Snowdonian and Cumbrian mountains, 
and still more is it so with the mountain fragments 
of the Highlands of Scotland, as irrefragably 
proved by the labours of our modern school of 
geologists, and the further fruitful labours of the 
survey since it cast off the meshes of the supposed 
succession of rocks woven and left us as an infor- 
mal legacy by the iate Sir Roderick Murchison. 
In addition to folding there has been discovered 
in these North-west Highland regions an extraor- 
dinary series of lateral dislocations and reversed 
faults which appear to be unique, and the effect of 
adaption by shearing instead of folding, to changed 
conditions cf space resulting from enormous lateral 
pressure. 
If however, we travel transversely from the 
centre of a great range, on one side if not on both, 
after crossing the outcrop of the strata and the 
“foot-hills,” we find that the beds which in the 
range proper are bent and contorted into violent 
folds take on more gentle undulations as we recede 
from the mountains until they recover in the plains 
ar almost horizontal position. 
Travelling towards the mountains, there is 
usually a gentle and long ascent before we reach 
their base — a feature noticeable in the eastern 
approach to the Andes and the Rockies, and also 
the French approach to the Alps. 
1 have now, I think, said sufficient to show the 
intimate connection that exists between the build- 
ing up or accretion of strata on the earth’s crust, 
and their after formation into mountains. 
But what arc really the relations of one to the 
other? Are they one of cau.-,e and effect? 
The upholders of the “contraction” theory 
recognised them as such, and met the difficulty by 
saying that the locus of accumulation is necessarily 
a weak place in the bosom of the earth, and 
therefore the earth’s crust in cr ishing-in squeezed 
and folded the unconsolidated deposit instead of 
the hard rock existing elsewhere. Till is an ex 
planation it will be w r ell to consider before 
broaching my own views on the subj*. t. At first 
sight it certainly seems to possess the defect of 
being too neatly contrived to meet the difficulty. 
It assumes what is not proved; for all great areas 
of sedimentation must, if the hypothesis be true, 
be w'eak places in the earth’s crust. 
Nature, unfortunately, is not arranged on ^o 
beautifully harmonious a system; and i‘ \.e on 
the true principles of geology inquire into v hat 
is taking place on the earth now, we have no 
grounds to suppose that such selective areas — if £ 
may use the term — are those to which sediments 
are universally carried. On the contrary . tl re 
appears to be an impartial distribution of sediment 
dependent on a vast variety of factors, ther or 
in addition to any that may be traced to a local 
weakness of the earth’s crust. As I have elsewhere 
shown* the North Atlantic is now' receiving 
directly or indirectly the drainage and detritus 
from about tAventy-one millions of square miles of 
land, or more than one-third the total land area f 
the globe. On the American or western side, on 
which there must now exist beneath the surr ice 
of the ocean enormous geologically recent and, - > 
to speak, unused deposits, w r e have some of t ut- 
most stable land on the globe, as instar.ee th 
Archtean Crystalline rocks of Canada and the 
Brazils, while between them we have the volcanic 
and unstable basin of the Gulf of Mexico rec jiv- 
ing the drainage of the Mississipi. W hen we 
* Origin of Mountain Ranges, p. 306, 
