chief difficulties of the bowlder-clay formation are removed, when it is admitted that frequent and vast changes of the land and waters have taken place since the distribution of large erratics—that a great northern glacial continent has subsided—that the bottom of the sea over Britain and the adjacent continent has been raised into dry land, while the Alps and Jura, formerly at lower levels, have been considerably and irregularly elevated. The elevation of this stupendous chain of rocks, not by one but by a succession of upheavals and depressions ere they assumed their present position and grouping, is a point generally admitted, and not difficult to demonstrate. The Alps, for example, are folded all round with successive belts or zones of sedimentary matter, marking, as so many milestones at different points of altitude, the measure of increment attained during the intervals of their deposition. These belts contain each their own peculiar class of fossils which determine their relative ages. In succession, the several suites or families of rocks rest upon the inverted outcrop or inclined edges of the older groups. Thus the history of organic life upon the globe, the incoming of new races and the extinction of old ones, as contained in these deposits, becomes a scale of measurement of the elevations, disruptions, and ever-varying conditions of the inorganic crust, while in the inverted, dislocated state of the crust itself, we mark the several throes by which it was lifted above the waters. Not one of the fossiliferous beds enveloping the granitic and crystalline nucleus of the chain of the Alps but has been shifted out of its original horizontal position, and the shift of the subjacent having always preceded the deposition of the overlying formation, it follows that, in addition to the intumescence of the chain, there must have been a series of oscillatory and elevatory movements before attaining its final altitude. But after the consolidation of the whole rocky strata, and while the waters were still many thousands of feet in depth, the superficial accumulations were being deposited—the bowlder drift, and erratic blocks, either by icebergs or other causes, were floated into position—and it was not until every one of these traveled stones, fresh even now as when torn from the living rock, were quietly settled down into the bottom of the sea, that Mont Blanc had displayed a moiety of its massive outline, or towered to one-half of its present colossal grandeur. The elevation of Ben-Mac-Dhui dates from the era of the old red sandstone formation. Mont Blanc was invaded on all sides by a sea that received the latest of the tertiary deposits. Both were submerged during the cataclysm which produced the bowlder clay; but as no increment to its bulk was derived from this cause, Ben-Mac-Dhui falls geologically to be reckoned a completed, and therefore a far older, mountain than Mont Blanc, which had not attained its full altitude and