In the west of England the Old Red Sandstone stretches from Hereford and Monmouth into the neighbouring Welsh counties of Brecknock and Glamorgan. It is here at its greatest thickness of nearly two miles. The lower part consists of red and yellow sandstones, marls, and shales, with a certain kind of limestone concrete. The red colour is due to iron, and wherever this is abundant fossils are scarce, though remains of fishes have been found in it. Scotland is the classic ground of the Old Red Sandstone, for it was here that Hugh Miller, when a working mason at Cromarty, first collected its wonderful fossil fishes. Hugh Miller's discovery is one of the romances of geological annals. "Let any one picture to himself," wrote the late Mr. Bristow, "the surprise he would feel should he, on taking his first lesson in geology, and on first breaking a stone--a pebble, for instance, exhibiting every external sign of a water-worn surface--find, to appropriate Archdeacon Paley's illustration, a watch, or any other delicate piece of mechanism, in its centre. Now this, many years ago, is exactly the kind of surprise that Hugh Miller experienced in the sandstone quarry opened in a lofty wall of cliff overhanging the northern shore of the Moray Frith. He had picked up a nodular mass of blue Lias limestone, which he laid open by a stroke of the hammer, when, behold! an exquisitely shaped Ammonite was displayed before him. It is no surprising that henceforth the half mason, half sailor, and poet, became a geologist. He sought for information, and found it; he found that the rocks among which he laboured swarmed with the relics of a former age. He pursued his investigations, and found, while working in this zone of strata all around the coast, that a certain class of fossils abounded; but that in a higher zone these familiar forms disappeared, and others made their appearance. "He read and learned that in other lands--lands of more recent formation--strange forms of animal life had been discovered; forms which in their turn had disappeared, to be succeeded by others, more in accordance with beings now living. He came to know that he was surrounded, in his native mountains, by the sedimentary deposits of other ages; he became alive to the fact that these grand mountain ranges had been built up grain by grain in the bed of the ocean, and the mountains had been subsequently raised to their present level by the upheaval of one part of its bed, or by the subsidence of another...." _The Old Red Sandstone_, a book which was the result of Hugh Miller's researches, is a geological classic.