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age so often associated with folded structure. Slaty cleavage, as has been demonstrated by experiment, as well as by field observation, is produced by a mashing together of the whole rocky mass in a direction at right angles to the cleavage plane and a corresponding extension in the direction of the dip of these planes. Now since the cleavage dip is usually nearly or quite vertical, this means a mashing together horizontally and a proportionate extension vertically. The amount of mashing together horizontally and extension vertically has been in many cases somewhat accurately estimated. In this case also, as in folding, we have evidence of a mashing of two or even three into one and a corresponding extension vertically of one into two or even three. This amount of extension affecting thick strata is sufficient to account for the highest mountains in the world without resorting to any hypothetical force pushing upward from beneath.

There seems therefore to be no reasonable doubt that mountains are formed wholly by lateral crushing with proportionate up-swelling. This is a very important point gained. Let us hold it fast. This brings me naturally to the next point.

Inferences from 5 and 6, Granitic Axis and Asymmetric Form.—A granitic or metamorphic axis is a very general, though not a universal, characteristic of mountains. The old idea (still held by some) was that fused matter was pushed up through and appeared above, the parted strata along the crest as the granite axis, lifting the strata, as it were, on its shoulders to form the slopes. But it must be observed that the axis is often only metamorphic, not granitic, and moreover that some mountains are composed wholly of folded strata alone. If, therefore, we regard granite as often only the last term of metamorphism, we may more properly speak of the axis of mountains as metamorphic. If so, then it is not necessary to suppose any vertical uprising of fused matter by volcanic forces at all. On the contrary, we would explain the axis thus:

It is evident that accumulating sediments must cause corresponding rise of the interior heat of earth toward the surface so as to invade the lower parts of the sediments and their included