horizontal base which subtended the transition strata of slate when they were deposited was only about twice the extent of base which now subtends them, that therefore the strata of gneiss were deposited upon a globe, the magnitude of which was greater than that upon which the transition strata of slate were deposited, and because of this the strata of gneiss suffered a greater contraction of base than the transition strata of slate while adjusting themselves to the nucleus of a globe which, since their formation, had constantly diminished in magnitude?

77. If so, what was the magnitude of the globe when the transition strata of slate were deposited?

78. The alterations that have taken place in the position of strata since they were deposited have been referred by geologists to the intrusion of igneous matter into the crust of the earth. The undulations of the strata are supposed to have been induced by that lateral pressure which the adjacent rocks would undergo when a disruption of the strata took place in the formation of the fissure through which the igneous matter was discharged. The strata represented in Fig. 14 have by their inflections suffered a contraction of horizontal base, equal in extent to four miles and a half. This contraction of the base

could not have been greater than was commensurate with the width of the fissure through which the molten matter was discharged. Now in geological sections, the fissures through which the igneous matter is discharged, are represented as not of great width, and quite inadequate to have induced by a lateral pressure those undulations which often extend over a whole district of country.

79. What is true in respect to the primitive and transition strata holds true in respect to the secondary and tertiary classes of rocks, inasmuch as the horizontal base which subtended those strata when they were deposited was greater than the horizontal base which now subtends them, while this difference in respect to the horizontal base of the tertiary strata is less than that of the secondary rocks; and, as a general law, the difference is always the greater, according to the seniority of strata in respect to the period of their deposition. How is this? May it not be explained, as before, upon the supposition, that, during the formation of the crust of the earth, the nucleus of the globe has ceased not to undergo a constant increase of density, and therefore a constant diminution of magnitude?

80. What has been the cause of that want of conformability which is found so often to occur

between the strata of two consecutive geological systems? How came it that after the last member of a geological system had been deposited, the strata of that system shifted from a horizontal position to one so much inclined to the horizon that the first member of the subsequent formation was deposited upon the edges of those strata?

FIG. 15.

Was it,

that during the interval which elapsed between the deposition of one geological system and the commencement in the deposition of another-the next in succession-the sun was darkened; and as the earth during the period in which the solar rays were withdrawn would radiate heat to distant space, and receive no heat ab extrá in return, the globe would suffer so great a diminution of temperature that its

density would increase, and therefore its magnitude would diminish; and because of this, the strata last deposited, when subjected to that lateral pressure which is induced at the circumference of a sphere while that sphere undergoes a diminution of magnitude, would shift from a horizontal to an inclined position, while adjusting themselves to the nucleus of a globe which had thus diminished in magnitude? Is it thus that the strata of one formation are so often found to lie uncomformable with the strata of a prior formation upon which they are recumbent ?

The questions which follow in reference to the alteration that has taken place in the position of strata since the period of their deposition, are inserted from a paper which I contributed to "Blackwood's Magazine," and which appeared in the October number of that journal so long ago as 1819, entitled "Predictions by C. C."

81. How is it "that strata which were originally horizontal in their position are now inclined to the horizon?" Is it because "our globe has suffered a constant diminution of magnitude since the strata were deposited which everywhere encompass it; and, therefore, since those strata at their formation would form as it were the circumference of a larger globe, and are now circumscribing the nucleus of a

less, they would, if soft, suffer bendings and inflections while accommodating themselves to a globe constantly diminishing in magnitude; and if indurated, they would break asunder, and assume a position somewhat inclined to the horizon; and as the globe diminished more and more in magnitude, the strata would approach more and more to a vertical position?"

82. How is it that "strata deviate the more from the horizontal position as they are the more ancient ?" "If this globe has constantly diminished in magnitude, then the more we recede from the present period the greater will be its magnitude, and, consequently, the more ancient the strata, the greater would be the globe upon which they were deposited. Since, therefore, strata, according to their seniority, would, when deposited, form as it were the circumference of a larger globe, and they are now all investing the same nucleus, and that the nucleus of a less, it is evident that the strata last formed would require to shift less from their original horizontal position, in order to accommodate themselves to the present magnitude of the globe, than strata of a prior formation; that, therefore, the more ancient the strata, the more must they be displaced from their first position: the primitive strata must have there