Having imposed upon himself the task of examining in detail the various fossiliferous formations of Scotland, our author extended his inquiries into the mainland of Orkney, and resided for some time in the vicinity of the busy seaport town of Stromness, as a central point from which the structure of the Orkney group of islands could be most advantageously studied. Like that of Caithness, the geology of these islands owes its principal interest to the immense development of the Lower Old Red Sandstone formation, and to the singular abundance of its vertebrate fossils. Though the Orkneys contain only the _third_ part of the Old Red Sandstone, which, but a few years ago, was supposed to be the least productive in fossils of any of the geological formations, yet it furnishes, according to Mr. Miller, more fossil fish than _every_ other geological system in England, Scotland, and Wales, from the Coal Measures to the Chalk, inclusive. It is, in short, “_the land of fish_,” and “could supply with ichthyolites, by the ton and by the ship-load, the museums of the world.” Its various deposits, with the curious organisms which they inclose, have been upheaved from their original position against a granitic axis, about six miles long and one broad, “forming the great back-bone of the western district of the Island Pomona; and on this granitic axis, fast jambed in between a steep hill and the sea, stands the town of Stromness.” The mass or pile of strata thus uplifted is described by Mr. Miller as a three-barred pyramid resting on its granite base, exhibiting three broad tiers—red, black, and gray—sculptured with the hieroglyphics in which its history is recorded. The great conglomerate base on which it rests, covering from 10,000 to 15,000 square miles, from the depth of from 100 to 400 feet, consists of rough sand and water-worn pebbles; and above this have been deposited successive strata of mud, equal in height to the highest of our mountains, now containing the remains of millions and tens of millions of fish which had perished in some sudden and mysterious catastrophe.