and Power; both as infinitely surpassing the most exalted faculties of the human mind as the mechanisms of the natural world, when magnified by the highest microscopes, are found to transcend the most perfect productions of human art." The Caradoc group. The second member of the Silurian series of deposits, following the ascending order, comprises sandstones of different colours, with occasional subordinate courses of calcareous matter. The strata constitute ranges of eminences, abutting against the trappean chain of the Caradoc hills in Shropshire. They are largely developed also in Montgomeryshire and Denbighshire, forming mountainous masses and picturesque knolls, upon one of which Powis Castle is built. Beds of quartz occur frequently where trappean rocks have cut through the sandstones; which are, no doubt, the ordinary strata of the district altered by the action of heat. A remarkable ridge on the east of the Caradoc, called Hoar Edge, is a quartzose mass of this description, consisting of sandstones fused by the great plutonic outburst of the Caradoc itself: and the extraordinary Stiper Stones supply another example of metamorphic sandstone, thrown into irregular serrated piles, like rugged cyclopean ruins, protruding from elevated moorlands in immediate contiguity to unaltered strata, exhibiting fine woodland scenery. Among the organic remains of the sandstone, trilobites of several species are abundant; a woody ravine, upon the property of Lord Clive near Welch Pool, so abounding with them, and with beautiful casts, that Mr. Murchison honoured the nameless site by calling it the "Trilobite Dingle." Several species of shells belonging to the genus Terebratula (bored, alluding to the perforated beak,) are of common occurrence. Shells of this kind form a numerous family, and have been denominated the Fossil Aristocracy, from the incalculable antiquity of their lineage. They are found in great numbers in the chalk, but of different 1. Terebratula furcata. 2. Terebratula neglecta. 3. Terebratula unguis. 5. Terebratula decemplicata. 6. Terebratula tripartita. species to those in the Silurian strata. Of corals, the chief remains belong to the tribe of Favosites, zoophytal organisations that appear to have swarmed in the Silurian seas, the formations consisting of a congeries of diverging or ascending parallel, prismatic, and porous tubes. An example of two species is given, the tubes of which vary considerably in size. Beautiful specimens have been figured from Eifel and Groningen, and from the Silurian strata of the Ohio and Niagara, where the cells are filled up with calcareous spar. Varieties of the genus Cyathophyllum also occur, but more plentifully, in the superior rocks of the system. The Wenlock group.-We now come to the Upper Silurians, the lower members of which consist of shale and limestone. The shale is a dull, argillaceous deposit, with occasional concretions of impure limestone, extensively developed in the neighbourhood of the town of Wenlock. It has its equivalent in the shale of Dudley. In the former locality it appears continuously in the longitudinal valley reaching from the Severn to the Onny, running in a line parallel to the ridge called Wenlock Edge, and intermediate between it and the Caradoc hills. The lower part of the shale contains concretions, which exhibit, upon being broken, an internal structure similar to the "cone-in-cone," common to the shale of the lias, the cones consisting of dark-coloured crystalline carbonate of lime in an argillaceous paste. The upper part, where exposed to the action of the atmosphere, has been deeply denuded. The Wenlock limestone is seen conspicuously in the Edge, which extends a course of about twenty miles, and forms one of the most remarkable features of the physical geography of Shropshire. The lime stone is disposed in two forms. It occurs in regular beds, termed "measures," of varying thickness, dull grey colour, more or less impure through the presence of argillaceous matter, the strata being often wavy and contorted. It occurs, also, in large concretional masses, where it is purer and more crystalline, (locally, they are called ball-stones,) which are sometimes dark blue, occasionally pink, freckled with veins and strings of white crystalline carbonate of lime. The ball-stones are frequently of immense size, having a diameter of thirty feet, and, in one case, a single mass has been quarried to the depth of eighty feet without its dimensions being ascertained. The annexed view of one of the quarries near Iron Bridge, shows the undulated and contorted beds of impure limestone, and the places from whence the crystalline variety, the concretions or ball-stones, have been extracted. The Wenlock shale, as a bed of passage, between the Upper and Lower Silurians, contains shells, corals, and trilobites, common to both; but the limestone is singularly rich in characteristic organic remains, among which are several species of Euomphalus, so named from the deeply umbilicated character of the disk. are univalve shells, internally divided into a series of partitions. As the animal increased in size, it deserted the innermost and smallest chamber, which was left vacant, and secreted a partition wall behind it; and as this process transpired at different stages of its growth, several successive chambers were formed. Those singular tenants of the deep, the Encrinites, belonging to the natural order of Crinoïdeans, or lily-shaped animals, of several varieties, occur, whose remains are so abundant in the ancient strata as to constitute formations many miles in extent and of a considerable thickness, entirely consisting of their calcareous skeletons. The animal is thus defined by Mr. Miller:-"A round, oval, or angular column, composed of numerous articulating joints, supporting at its summit a series of plates or joints, which form a cup-like body, containing the viscera, from whose upper rim proceed five articulated arms, dividing WENLOCK LIMESTONE. 1. Dimerocrinites decadactylus. 2. Cyathocrinites goniodactylus. 3. Cyathocrinites capillaris. 4. Hypanthocrinites decorus. 5. Dimerocrinites icosidactylus. into tentaculated fingers, more or less numerous, surrounding the aperture of the mouth." The two genera which have attracted most attention are those with a circular stem, or Encrinites, most nearly resembling the external form of the lily; and the Pentacrinites, which have the stem pentagonal. The engravings represent some of the Silurian varieties. All the species in the older rocks have the circular stem, with but one exception; and all became extinct before the formation of the lias, new groups succeeding, which have now dwindled down to two analogues, which inhabit our existing seas. The animal occupied a fixed position at the bottom of the ocean, like its modern representatives, or was attached to floating pieces of wood, merely moving itself as far as it could reach by bending its very flexible column, which was admirably adapted for this purpose. This stem, which may be called the vertebral column, although the Encrinites are invertebrated, consists of a vast number of ossicula, little bones or joints, with a central perforation, so as to admit of being strung together when found detached. They commonly occur singly in the northern counties, passing under the denominations of " wheel-stones," and "St. Cuthbert's beads," from having been strung as beads, and formerly used as rosaries. Hence the lines in Marmion: "On a rock by Lindisfern St. Cuthbert sits, and toils to frame The sea-born beads that bear his name." Dr. Mantell states that he has found these circular perforated ossicula, which had been worn as ornaments, in tumuli of the ancient Britons; and also, that the "channel formed by the united ossicula of the column, has given rise to the curious fossils called in Derbyshire screw or pulley stones, which are flint casts of these cavities. They occur in the beds of chert which are interstratified with the mountain limestone; the siliceous matter, when fluid, filled up the channels, and invested the stems: the calcareous substance has since been dissolved and removed, and solid cylinders of flint, resembling a pulley, remain. In the quarries on Middleton Moor, near Cromford, where extensive beds of limestone, composed of crinoideal remains, are worked for chimney-pieces and other ornamental purposes, beautiful examples of these fossils may be obtained. The cavities of the column and ossicula are often filled with white calcareous spar; while the ground of the marble is of a dark reddish-brown colour." Man now erects his mansion, and has its apartments adorned with variegated slabs, little imagining that the component parts |