674 



GEOLOGY. 



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 



species to those 

 in the Silurian 

 strata. Of co- 

 rals, the chief 

 remains belong 

 to the tribe of 

 Favosites, zoo- 

 phytal organisa- 

 tions that appear 

 to have swarm- 

 ed in the Si- 

 lurian seas, the 

 formations con- 

 sisting of a con- 

 geries of diverg- 

 ing or ascending 

 parallel, prisma- 

 tic, 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 



Terebratula furcata. 

 2. Terebratula neglecta. 



3. Terebratula unguis. 



4. Terebratula pusilla. 



5. Terebratula decemplicata. 



6. Terebratula tripartita. 



