same, would continually decrease in proportion as the detritus accumulated on the surface and protected it from the action of destructive chemical and mechanical agents. A thin layer of loam, sand, or gravel, would have been a shield against the decrystallizing action of the atmosphere and erosion by water. This is shown by the fact that granite rocks that have been cut and scored by the passage over them, as it is supposed, of icebergs armed with boulders, and afterwards buried by drift, on the removal of the soil with which they have been covered, exhibit no indications of having undergone disintegration after they had received those marks. Many of those, indeed, that have been exposed to the action of the elements appear unaltered. The grooves ploughed across them are as smooth and well defined as they can be believed to have been when first made.

It is shown also by the failure of the most powerful streams to produce any important change on the height or form of the granite rocks over which they have run for thousands of years. Let any one examine the granite rocks that in many places lie at the bottom of the rapid streams of New England, and form the dykes over which they fall, and he will find them generally free from any marks of disintegration or erosion by the grinding of sand, pebbles, or ice. The cavities that are cut where the water rushes down rapids or over falls, are caused by the whirl of gravel

and pebbles in depressions, not by the mere passage of the stream. This is indicated by Humboldt in respect to the great cataracts of the Orinoco, formed by granite dykes, that have not been worn away, he represents, in any perceptible measure by the rush of that vast volume of water.

"When seated on the bank of the Oroonoko, our eyes are fixed on those rocky dykes, the mind inquires whether, in the lapse of ages, the falls change their form or height. I am not much inclined to believe in such effects of the shock of water against blocks of granite and in the erosion of silicious matter. The holes narrowed towards the bottom, the funnels that are discovered in the raudales, as well as near so many other cascades in Europe, are owing only to the friction of the sand and the movement of quartz pebbles.

"We will not deny the action of rivers and running waters when they furrow friable ground covered with secondary formations. But the granite rocks of Elephantine have probably no more changed their absolute height during thousands of years than the summits of Mont Blanc and of Canigou. When you have closely inspected the great scenes of nature in different climates, it is impossible not to admit that those deep clefts, those strata raised on end, those scattered blocks, those traces of a general convulsion, are the results of extraordinary causes, very different from those which act slowly on the surface of the globe in its present state of tranquillity and repose. What the

waters carry away from the granite by erosion, what the humid atmosphere destroys by its contact with hard and undecomposed rocks, almost wholly escapes our perception; and I cannot believe, as some geologists admit, that the granitic summits of the Alps and the Pyrenees lower in proportion to the accumulation of pebbles in the gullies at the foot of the mountains. In the Nile, as well as in the Oroonoko, the rapids may diminish their fall, without the rocky dykes being perceptibly altered."-Humboldt's Narrative, vol. v. pp. 62, 64, 65.

The supposition, then, that such granitic continents could ever be disintegrated and transported to the ocean by the chemical and mechanical agents that are now acting on the surface of the earth, is altogether untenable. Such indestructible masses stretched along the line of the ancient seas could no more have furnished the materials of our strata than though they had been stationed in another world. Geologists themselves could never have advanced such an hypothesis had they properly considered the impracticable conditions it involves.

Admitting, however, that those imagined continents of granite could have been disintegrated by the chemical and mechanical agents to which they would have been subjected, and the theory is still embarrassed by the equally fatal objection, that they would not even then have furnished the materials of the stratified rocks; inasmuch as some of the most im

portant of the mineral substances that enter into their composition are not constituents of granite, except in quantities almost too slight to be appreciable.

Granite is composed either of quartz, felspar, and mica, or quartz, felspar, and hornblende; and usually in the proportion of two parts of quartz, two or three of felspar, and one of mica, or hornblende; and consists, when mica is an element, of 74 to 75 per cent. of silica, 13 to 14 of alumine, 8 or 9 of potash; and four or five other ingredients, amounting together to the remaining four or five per cent. The quantity of lime is less than half of one per cent., and of iron, less than two. When hornblende is an element, the potash is diminished one half, the lime increases to near five per cent., and the iron to near three; and these elements are not promiscuously blended, but the quartz, felspar, and mica, or hornblende, are separately crystallized and united in that form in a compact mass.* On the supposition, then, that such mountains and continents of granite could have been decrystallized and transferred to the bed of the ocean, they could not have contributed to the formation of any strata except those of which silica and alumine are the constituents; that is, gneiss, quartz rock, sandstones, shales, and sand and gravel. They could have furnished nothing, except on a scale too insig

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nificant to merit consideration, towards the structure of the vast beds of limestone, iron, chalk, salt, and several other important deposits.

The theory thus fails again to fill the office for which it is devised, and on a vast scale. Grant them all that it can yield, exhaust its utmost resources, and instead of supplying, as it professes, the whole of the materials of which the strata are constituted, it can only furnish from one-half to two-thirds. How fatal to their system this defect is, is seen from the fact that limestone, to the formation of which it could contribute nothing, occurs among the lowest of the stratified rocks, and alternates either with sandstones, shales, or coal, throughout the whole series of the primary, secondary, and tertiary groups, extends over immense areas, and is often of great depth.

"One of the most remarkable geological features of this continent is the vast extent of the carboniferous limestone. I have traced its eastern border-conforming to the course of the other mineral formations east of the Mississippimore than one thousand miles running to the west of south, from the State of New York to the thirty-fifth degree of north latitude in the State of Alabama; the course is there changed, and lies to the north of west, leaving Little Rock on the Arkansas about thirty miles to the south, and disappearing between five and six hundred miles from the Rocky Mountains. This deposit extends uninterruptedly a geographical distance of at least 1,500 miles from east to west;