_Onu_.--Having resided for a long time in Edinburgh, and having heard a number of discussions on the theory of Dr. Hutton, or the plutonic theory of geology, and having been exceedingly struck both by its simplicity and beauty, its harmony with existing facts, and the proofs afforded to it by some beautiful chemical experiments, I do not feel disposed immediately to renounce it for the views which I have just heard explained; for the principal facts which our new acquaintance has stated are, I think, not inconsistent with the refined philosophical systems of Professor Playfair and Sir James Hall. _The Unknown_.--I have no objection to the refined plutonic view, as capable of explaining many existing phenomena; indeed, you must be aware that I have myself had recourse to it. What I contend against is, its application to explain the formations of the secondary rocks, which I think clearly belong to an order of facts not at all embraced by it. In the plutonic system there is one simple and constant order assumed, which may be supposed eternal. The surface is constantly imagined to be disintegrated, destroyed, degraded, and washed into the bosom of the ocean by water, and as constantly consolidated, elevated, and regenerated by fire, and the ruins of the old form the foundations of the new world. It is supposed that there are always the same types, both of dead and living matter; that the remains of rocks, of vegetables, and animals of one age are found embedded in rocks raised from the bottom of the ocean in another. Now, to support this view, not only the remains of living beings which at present people the globe might be expected to be found in the oldest secondary strata, but even those of the arts of man, the most powerful and populous of its inhabitants, which is well known not to be the case. On the contrary, each stratum of the secondary rocks contains remains of peculiar and mostly now unknown species of vegetables and animals. In those strata which are deepest, and which must consequently be supposed to be the earliest deposited, forms even of vegetable life are rare; shells and vegetable remains are found in the next order; the bones of fishes and oviparous reptiles exist in the following class; the remains of birds, with those of the same genera mentioned before, in the next order; those of quadrupeds of extinct species, in a still more recent class; and it is only in the loose and slightly consolidated strata of gravel and sand, and which are usually called diluvian formations, that the remains of animals such as now people the globe are found, with others belonging to extinct species. But in none of these formations, whether called secondary, tertiary, or diluvial, have the remains of man or any of his works been discovered. It is, I think, impossible to consider the organic remains found in any of the earlier secondary strata, the lias-limestone and its congenerous formations for