Cornbrash-- Feet. Lower Oolite and Upper Lias, as proved by bore-hole on Gerrick Moor, 950 Middle and Lower Lias, ascertained from measurement of cliff-sections and from mining operations to be more than 850 New Red Sandstone and Marl, found by boring close to the Tees to exceed 1,600 Magnesian Limestone, at least 500 Coal-measures, possibly absent 0 Millstone Grit, not less than 500 Carboniferous Limestone series at least 3,000 Silurian rocks, probably not less than 10,000 ------- 17,400 There is thus evidence that this dyke has risen through probably more than three miles of stratified rocks. How much deeper still lay the original reservoir of molten material that supplied the dyke, we have at present no means of computing. 12. EVIDENCE AS TO MOVEMENT OF THE MOLTEN ROCK IN THE FISSURES It is usual to speak of the molten material of the dykes as having risen vertically within the fissures. And doubtless, on the whole, the expression is sufficiently accurate. In the case of such long dykes as those of Central Scotland and the North of England, where the petrographical character of the material remains so uniform throughout, it is obvious that the andesite or dolerite cannot have come from a mere single pipe like a volcanic orifice. Nor can we easily understand how it could have been supplied even from a series of such pipes. The general aspect and structure of the dykes suggest that the fissures were rent so profoundly in the crust of the earth as to reach down to a reservoir of molten rock which straightway rose in them. The roof of such a reservoir, however, may have been irregular and uneven, so that a fissure need not have traversed it continuously, but may have only touched its upward projecting vaults. Hence gaps would arise in the continuity of the dyke-material. The ascent of lava from a line of such separate openings along a fissure would necessarily involve lateral as well as vertical movements in the molten mass which would be forced along the open rent until the several streams united and filled it up. We might therefore expect somewhere to find instances of flow-structure in the dykes pointing to these movements. I have already referred to the lines of amygdales frequently noticed in dykes, especially towards the centre. Occasionally these steam-vesicles may be observed to be drawn out in one general direction indicative of the trend of motion of the molten rock.