British Association, Edinhurgh fleeting — Lcqncorth. 241 
depression). Every upward swirl and eddy has its answering downward 
swirl. The whole surface of our globe is thus broken up into fairly 
continuous and paired masses, divided from each other by moving 
areas and lines of mountain making and crust movement, so that the 
surface of the earth of the present day seems to stand midway in its 
structure and appearance between those of the sun and the moon, its 
eddies wanting the mobility of those of the one and the symmetry of 
those of the other. In the geology of the earth-crust, also, the inter- 
crossing of the two sets of folds, theoretically at right-angles to each 
other, gives rise to effects equally startling. It lies at the origin of the 
thrust-plane or over-fault, where the septal region of contrary motion 
in the fold becomes reduced to, or is represented by, a plane of contrary 
motion. It allows us to connect together under one set of homologies 
folds and faults. The downthrow side of the fault answers to the 
trough, the upthrow side to the arch, of our longitudinal fold; while the 
fault-plane itself represents the septal area reduced to zero. The node 
of the fault, and the alternation and alteration of throw, are due to the 
effects of the transverse folding. 
These transverse folds of different grades, which affect different layers 
of the earth-crust differentially, account also for the formation of lacco- 
lites, of granitic cores, and of petroiogical provinces ; and they enable us 
also to understand many of the phenomena of metamorphism. 
Of the folds of the third order I shall here say nothing ; but I must 
frankly admit that the primal cause of all this tangential movement and 
folding stress is still as mysterious to me as ever. I incline to think 
that it is due to many causes— tidal action, sedimentation, and many 
others. I cannot deny, however, that it may he mainly the result of the 
contraction in diameter of our earth, due to the loss of its original heat 
into outer space. For everywhere we find evidences of symmetrical 
crushing of the earth-crust by tangential stresses. Everywhere we find 
proofs that different layers of that crust have been affected differentially, 
and the outer layers have been folded the most. We seem to be dealing 
not so much with a solid globe as with a globular shell composed of 
many layers. 
Is it not just possible after all that, as others have suggested, our earth 
is such a hollow shell, or series of concentric shells, on the surface of 
which gravity is at a maximum, and in whose deepest interior it is non- 
existent? May this not be so also in the case of the sun, through whose 
spot eddies we possibly look into a hollow interior? If so, perhaps our 
present nebula- may also be hollow shells formed of meteorites ; on the 
surfaces of these shells the fiery spirals we see would be the swirls which 
answer to the many twisting crustal septa of the earth. Our comets, too, 
in this case might be elongated ellipsoids, whose visible parts would be 
merely interference phenomena or sheets of differential movement. 
In this case we have represented before us to-day all the past of our 
earth as well as its present. Uniformity and evolution are one. 
Thus from the microscopic septa of the laminsu of the geological for- 
mations we pass outwards in fact to these moving septa of our globe. 
