NATURAL HISTORY OF THE PRIMEVAL WORLD. 



LOWER SILUKIAN GKOUP. 



rssijsr-.^'srts 



Dark-coloured slates, calcareous ) 



flags, sandstones, . . . .( D ' d ' 



\ Brachiopods ; Lamelli- 



Shelly sandstones; conglomerate/ branchiata; Pteropods; 

 and shales; Bala limestone, . ,f" Cystideans; Grapto- 

 ) lites; Trilobites. 



UPPER SILURIAN PERIOD. 



During the later ages of the Silurian period some 

 new genera of fishes made their appearance in the 

 shallow ocean. " The so-called fish-bones," says Figuier, 

 " have been the subject of considerable doubt. Between 

 the Upper Ludlow rocks, opposite the castle of Ludlow, 

 and the next ascending stratum, occurs a thin bed of 

 soft, earthy shale and fine, soft, yellowish greenstone, 

 immediately overlying the Ludlow rock : just below 

 this lies a remarkable animal deposit, called the Ludlow 

 bone-bed, from its large deposits of the bones of 

 animals." Long before geology acquired form and 

 substance as a science, these bones attracted attention 

 and excited curiosity. The old poet, Michael Drayton, 

 refers to them in his Poly- Olbion : 



"With strange and sundry tales 



Of all their wondrous things; and not the least in Wales, 

 Of that prodigious spring (him neighbouring as he past), 

 That little fishes' bones continually doth cast." 



When Sir Roderick Murchison, who may justly be 

 entitled the great historian of Siluria, first examined 

 this deposit he found it to exhibit " a matted mass of 

 bony fragments, for the most part of small size and of 

 very peculiar character." These fragments were partly 

 of a mahogany hue, and partly of so brilliant a black, as 

 to convey the impression that the bed was a heap of 

 broken beetles. 



Professor Owen has given it as his opinion that 

 among the remains may distinctly be recognized those 

 of fishes. Other naturalists have controverted the pro- 

 fessor's statement, which, however, is supported by Sir 

 Roderick Murchison. Without entering into so vexed 

 a question, we may turn to the consideration of those 

 fossil relics which all observers have agreed in pro- 

 nouncing of a Crustacean character. 



The Trilobites, let us add, now attained their greatest 

 development, as in the species Calymene, Phragmoceras, 

 and Ilcenus. 



The Silurjan crustaceans were of a very curious 

 form, not altogether unlike the existing prawn. They 

 were inhabitants of the fresh waters, and endowed with 

 extraordinary voracity. The Scotch quarrymen called 

 them " Seraphim," from the winged form and feather- 

 like ornament of the thoracic appendage. 



The best known species are the Pterygotus lilolatus 

 and the Eurypterus, 



Now, too, first budded on the deep-sea rocks the 

 innumerable members of the order Crinoidea or Encri- 

 nites, commonly called " Stone Lilies." " We may 

 judge," says Dr. Buckland, " of the degree to which the 

 inhabitants of these species multiplied among the first 

 inhabitants of the sea, from the countless myriads of 

 their petrified remains which fill so many limestone 



beds of the Transition formations, and compose vast 

 strata of entrochal marble, extending over large tracts 

 of country in Northern Europe and North America. 

 The substance of this marble is often almost as entirely 

 made up of the petrified bones of Encrinites as a corn- 

 rick is composed of straws. Man applies it to con- 

 struct his palace and adorn his sepulchre; but there 

 are few who know, and fewer still who duly appreciate, 

 the surprising fact that much of this marble is composed 

 of the skeletons of millions of organized beings, once 

 endowed with life and susceptible of enjoyment, which, 

 after performing the part that was for awhile assigned 

 to them in living nature, have contributed their remains 

 towards the composition of the mountain masses of the 

 earth." 



The Crinoidean, or lily-shaped animal, is thus de- 

 scribed by Hugh 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 into tentaculated fingers, more or less num- 

 erous, surrounding the aperture of the mouth." 



There are several varieties, but the two most con- 

 spicuous and beautiful genera are 



The Encrinites, with a circular stem, very closely 

 resembling the external form of the lily ; and 



The Pentacrinites, which have a pentagonal stem. 



The former genus belongs to the older rocks, but all 

 its species became extinct before the Lias period, new 

 groups succeeding, which, in our modern seas, are 

 represented by only two types. 



The animal lived in a fixed position, attached to the 

 sea-bed or to some external object, moving itself in 

 quest of food by bending forward or downward its 

 flexible column. This column, or stem, consisted of 

 numerous ossicula, i.e., small bones, joints, or articula- 

 tions, which, being perforated in the centre, may be 

 strung together like beads. In our northern counties 

 they are very frequently met with, and are commonly 

 called " wheel stones," or "St. Cuthbert's beads:-." To 

 the latter appellation Sir Walter Scott refers in his 

 poem of " Marmion": 



" On a rock by Lindisfarne 

 St. Cnthbert sits, and toils to frame 

 The sea-born beads that bear his name." 



According to Dr. Mantell, they have been discovered 

 in the barrows or tumuli of the ancient Britons, who 

 appear to have used them as ornaments. 



From the same authority we learn that the channel 

 formed by the united ossicula of the column has origi- 

 nated the curious fossils called in Derbyshire screw or 

 pulley stones, which are, in fact, flint casts of these 

 cavities. They occur in the beds of chert interstrati- 

 fied with the mountain limestone; the siliceous matter, 

 when fluid, filled up the channels and surrounded the 

 stems: the calcareous substance has since been dis- 

 solved and removed, and solid cylinders of flint, resem- 

 bling a pulley, remain. "In the quarries on Middleton 

 Moor, near Cromford, where extensive beds of limestone, 

 composed of crinoidal remains, are worked for chimney- 

 pieces and other ornamental purposes, beautiful exam- 

 ples of these fossils may be obtained. The cavities of 



