Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/174

130 shales which, they traverse could have remained open and been filled from the water of the sea which deposited the overlying rocks, like the Liassic veins in the Carboniferous limestone of the Mendips so admirably described by Mr. C. Moore, seems altogether incredible. The explanation of the phenomenon which I would suggest is as follows:—that at the time when the upheaval which produced the fractures took place, the shales were already covered by beds of soft and unconsolidated sand, and that, as the fissures gradually opened, the sand as gradually found its way down into the interstices; finally the sand, both in the beds and the fissures, became consolidated into a hard rock.

From the details which I have now given, I believe that the following propositions on the subject may be considered fully established.

(1) The Secondary rocks lie indifferently against all the members of the Lower Palaeozoic series, from the Lower Silurian and associated granites up to the Upper Old Red Sandstone.

(2) The Secondary strata which are thus in contact with the Palaeozoic rocks are of very various ages, from the Trias to the Upper Oolite inclusive, and contain representatives of all the subdivisions of the Jurassic series, except perhaps the Upper Lias.

(3) There is a total absence in the Jurassic series of strata made up of fragments of the rocks against which they repose; and, on the other hand, the conglomerates, which are by no means rare in that series, are made up of fragments of rocks totally different from these.

(4) There are no indications whatever in this series of Secondary strata that, as we approach the Palaeozoic rocks, we are coming to an old shore-line.

(5) The Secondary rocks exhibit signs of having undergone great disturbance, being bent into numerous folds, broken up by many faults, and traversed by fissures filled with materials from above; their fossils are also much more frequently distorted by pressure than those of the equivalent strata in England.

(6) The evidence of disturbance and dislocation in the Secondary strata increases as we approach the Palaeozoic rocks, till at last the beds of the former are often found in a completely crumpled and crushed condition at the points of contact.

All these facts point to one conclusion—namely, that the Secondary strata of the north-east of Scotland owe their present positions and their consequent remarkable preservation from the denudation which has removed such enormous masses of contemporary deposits in this area, to great faults, which have thrown them down, probably several thousands of feet, below their original level. I find that Prof. Geikie has already arrived at this conclusion with regard