The majority of persons, merely acquainted with the name and position of the Scilly Isles, generally associate in their mind with the mention of this group a cluster of rugged rocks, affording shelter and sustenance to a few poor fishermen and pilots, and famous for nothing else than the frequent shipwrecks and naval disasters of which in times past they have been the scene. From their isolated position, and their comparative difficulty of access, they have been much less frequently visited, and less accurately described, than many other of the beautiful islets which surround our favoured shores; hence much misapprehension prevails both as to their extent and their capabilities, while very little indeed, of a scientific character, has been put on record with reference to their varied attractions, zoological, botanical, or geological.

In one of my last papers on the “Bottom-rocks” I appended a coloured map to a portion of the first dry-land of our mother-earth, a portion of the first division of the land from those waters “which covered the globe,” a fraction of one of those primeval cracks or ridges which then remotely shadowed out our present continents and oceans; and in the little green patches I gave all the traces known of the first beaches and sands which spread around those low and barren tracts in the great region of North America which I selected for an illustration. To this map I hope soon to add, as supplements, others of South America and of Europe. Africa must be left yet a long while ere one dare make the like attempt. To these maps, from time to time, I shall add colour after colour to show the successive deposition of those great rock-formations in which the animals and plants of the successive life-creations of our planet have been entombed; and I hope also to be able to give charts of the teeming oceans during each of those past wonderful ages severally characterised as the stages of progress and development of organic beings.

The paleontology or the study of the fossils of Hook Head is, if it be possible, even more interesting than its physical geology. As soon as ever we cross over the sandstones, and ascend into the higher strata of the Carboniferous series proper, we reach a domain abounding with animal life. Almost immediately above the sandstones which afford the remains of the fossil plants, we reach a zone having a distinct mineral character. This zone consists of a black shale, a substance which was originally black mud deposited by the sea, and this black shale is an important member of the great Carboniferous series of the south of Ireland. At Hook, it is a very degraded form of that member of the Irish carboniferous series known under the name of “carboniferous slate.” In this locality it has a thickness of only a few yards, but westward from Hook the carboniferous slate increases in thickness, until we find it in the county of Cork, separating the sandstone strata below from the lower portion of the carboniferous limestone above, by an interval, in some instances, reaching to about 4,000 feet. At Hook, this ancient muddy sea-bottom seems to have existed for a shorter time than towards the westward, and was succeeded by a sea containing a considerable portion of lime in its waters.

The beautiful specimen of Phacops caudatus, which we figure in Plate V., has long been in the private collection of Professor Tennant. It is from the Upper Silurian limestone of Dudley, and would be a perfect example but for the exception only of its having the segments of the body somewhat bent inwards, and slightly distorted from their natural positions by pressure. The lateral edges and their segments are unfortunately obscured by being embedded in the matrix, so that they cannot be accurately delineated.

This characteristic species of Trilobite was first noticed by Brunnich, in 1781, under the name of Trilobus caudatus. It was subsequently termed Asaphus caudatus by Brongniart, Dalman, Dr. Buckland, and other writers. Burmeister, however, in his valuable work on the “Organization of Trilobites,” called it Phacops caudatus, which generic determination modern palæontologists have followed.

There is probably no mineral, of all the many that contribute to England's commercial greatness, which is so varied in kind, chemical composition, and appearance, as coal; and an interesting volume might be written on the different forms under which it is extracted from the earth, under the names of brown-coal, oulm, cannel-coal, bituminous coal, anthracite, and the like. Next to the bituminous coals of Great Britain, the most important are the anthracites or stone-coals; and of these I propose to give a short sketch, especially as relates to their development in the coal-basin of South Wales. Of their importance commercially there can be no doubt: for, on referring to the “Mining Records” published during last year, I find that 960,500 tons were raised in this basin alone, for the purpose of supplying 18 blast-furnaces in the counties of Brecon, Glamorgan, and Caermarthen.

There is something about the margins of Ireland, as seen on a map, and even more so when these margins are visited, which gives to this island a peculiar rugged aspect. Its northern, western, and southern sides are penetrated by deep bays, and cut into prominent headlands by the force of the waves of the Atlantic; and this erosive power of the ocean has not only added much to the boldness and beauty of its coasts, but has also revealed to us much information concerning its physical structure, and the conditions under which many of its rocky masses were formed.