I am now to mention another appearance of a different kind. Those strata of marl are in general not much consolidated; but among, them there are sometimes found thin calcareous strata extremely consolidated, consequently much divided by veins. It is in the solid parts of those strata, perfectly disconnected from the veins, that there are frequent cavities curiously lined with crystals of different sorts, generally calcareous, sometimes containing also those that are siliceous, and often accompanied with pyrites. I am persuaded that the origin of those cavities may have been some hollow shells, such as _echini_ or some marine object; but that calcareous body has been so changed, that it is not now distinguishable; therefore, at present, I hold this opinion only as conjecture. Having, in my return to Edinburgh, traveled up the Tiviot, with a view to investigate this subject of primary and secondary operations of the earth, I found the vertical strata, or alpine schistus, in the bed of the river about two miles below Hawick. This was the third time I had seen those vertical bodies after leaving the mountains of Lauderdale. The first place was the bed of the river Tweed, at the new bridge below Melrose; but here no other covering is to be seen above those vertical strata besides the soil or traveled earth which conceals every thing except the rock in the bed of the river. The second place was Jedburgh, where I found the vertical strata covered with the horizontal sandstone and marl, as has been now described. The third place was the Tiviot, and this is that which now remains to be considered. Seeing the vertical strata in the bed of the river, I was desirous to know if those were immediately covered with the horizontal strata. This could not be discovered in the bed of the river where the rock was covered upon the banks with travelled earth. I therefore left the river, and followed the course of a brook which comes from the south side. I had not gone far up the bank, or former boundary of the Tiviot, when I had the satisfaction to find the vertical strata covered with the pudding-stone and marly beds as in the valley of the Jed. It will now be reasonable to suppose that all the schistus which we perceive, whether in the mountains or in the valleys, exposed to our view had been once covered with those horizontal strata which are observed in Berwickshire and Tiviotdale; and that, below all those horizontal strata in the level country, there is at present a body or basis of vertical or inclined schistus, on which the horizontal strata of a secondary order had been deposited. This is the conclusion that I had formed at Jedburgh, before I had seen the confirmation of it in the Tiviot; it is the only one that can be formed according to this view of things; and it must remain in the present state until more evidence be found by which the probability may be either increased or diminished.