The geological system of the illustrious Hutton assumed as an essential principle, that as the present continents and dry land were once the bottom of the ocean, and have been formed, either in greater part or entirely, of fragments of pre-existing continents now submerged, so is the work of destruction and renewal still continuing, the substance of our present dry land being loosened, abraded, or worn down by meteoric agencies, and carried by torrents and rivers to the ocean, to be there by currents distributed over the bottom of the sea, and by internal heat consolidated into new strata, which in time will be elevated into new continents and islands. To apply this theory in the case of the Jura boulders, Playfair assigned their transport to an epoch anterior to the formation or excavation of the deep valleys and lakes which would now form an insurmountable obstacle to such transport, and thus obtained a greatly inclined plane, extending from the summit of the Alps to the Jura, on which to trundle the fragments gradually downwards, by aid of the numerous streams and torrents descending from the higher to the lower ground. But as this theory would, as thus applied, premise that the land had been raised above the sea-level prior to the transport of the boulders, no means of effecting the great excavations, including the Lakes of Geneva and Neufchatel, which are supposed to have been formed subsequently, are left, except the slow erosive action of rains, frost, torrents, and such-like agents--means which few will consider adequate to the desired object; and hence the explanation of Playfair, resting solely on a bold hypothesis, must be rejected. As most of the preceding theories referred to the usually rounded condition of the granite boulders (many boulders of other rocks are angular), as an evidence of movement through the agency of water, De Luc, preparatory to the promulgation of his own theory, thought it expedient to show that blocks of granite, even as they stand tranquilly braving the storms, are gradually weathered into a rounded form. He thus cites the granite of Darmstadt as an example:--“Here I found a striking example of the manner in which blocks and even rocks of granite are rounded by the decomposition of the angles of their masses. I perceived it first in some angular pieces that had been detached and lay at the foot of the rock, surrounded with rubbish; for, on giving them a strong blow with an iron at the end of my stick, the angles fell off, detaching themselves with a concave surface on their inner side; and I thus produced rounded blocks, exactly resembling those which I had seen scattered on the plains.” This spherical concretionary structure has been noticed in the granite of Dublin and Down, and is common in trap rocks. Having smoothed away this difficulty, De Luc tacks on the boulders as a corollary to his theory of subsidences. Immense masses of strata, subsiding into huge caverns or hollows beneath them,