Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/218

 through the marl is a subsidiary argument of no small weight: these tubes, some of which are very thin and scarcely an eighth of an inch in diameter, with a length of twelve inches, are in a position perpendicular to the plane of the stratum, which, when this latter is at an angle of 40°, causes the coralline tubes to form with the plane of the horizon an angle of 50°; a situation by no means agreeable to the known habit of this class of animals which always affects a vertical position with regard to the horizon.

If then it be conceded that these beds have undergone a vertical motion, what remains is to collect the local probabilities relative to each of the two methods, by which, as already described, mineral beds are elevated or depressed.

The principal argument in favour of motion by depression, is the absence of any unstratified rock between the elevated stratum and that which naturally lies below and in contact with it; to which may be added the fracture and disturbance of those superincumbent beds which lie on the dip of the elevated stratum. These circumstances, however, are directly the opposite of those which take place at the Steeraway-hill; for, in the first place, the coal strata that lie upon the limestone crop out with perfect regularity, and nearly horizontal, along the opposite side of the valley, parallel to the hill and not more than two hundred yards from it, a line which, on the hypothesis of depression, would be the precise situation of the principal disturbance. Secondly, the beds of limestone and sandstone, which a hundred yards south of the Steeraway are found with an elevation of about 24° and resting immediately on a soft and sandy slate clay, are in the Steeraway itself tilted up at an angle of 40°, with a great mass of greenstone interposed between them and the slate clay. Is it not therefore probable that the greenstone has occupied the situation which it now holds, posteriorly to the formation of the stratified