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HARDWICKE'S SCIENCE-GOSSIP. 



[Oct. 1, 1S70. 



no less than twenty different stages, from the egg 

 to the adult animal. In the last condition its 

 body was enclosed in tri-lobed joints, which served 

 as a defence, and at the same time were flexible 

 enough to be adjusted to all the motions of their 

 possessor. In fact, they served all the purposes of 

 an ancient coat of mail. These various species of 

 Trilobites literally swarmed in every sea of the 

 Silurian period. There were species alike peculiar 

 to deep water and to shallow, and the rocks formed 

 under these different conditions (as I have above 

 related) indicate which these species were. Well 

 do I remember them crawling over the oozy sea- 

 bottom, gorging the mud, as I am told earthworms 

 now do, for the sake of the animalculous matter 

 dispersed through it. When any danger approached, 

 they coiled themselves up like modern wood-lice, 

 and, in this state, you may not unfrequently find 

 them fossilized. When the adult animal moulted, 

 he did so at the junction of the head and carapace ; 

 and this accounts for the myriads of detached heads 

 and tails found in every piece of Silurian limestone 

 or shale. The Trilobite had compound eyes, 

 arranged on sessile, half-round stalks, iu which 

 they were set like so mauy mounted jewels. Some 

 species had not less than four hundred of these 

 distinct facets. Thus we find the structure of this 

 little creature completely setting all those wild 

 theories at defiance in which some people have 

 indulged. Their eyes indicate a similar constitution 

 of the atmosphere then to what it is now, for the 

 passage and refraction of the rays of light. And 

 this fact is supplemented by the sun-cracks, rain- 

 drops, &c, which pit the sandstones, telling of 

 meteorological action identical in its operation with 

 the present. Indeed, all the facts go to prove that 

 even at this distant epoch of the world's history, 

 the light of the sun and the atmosphere of the earth 

 were exactly like what they are at present. 



During the period of the " Middle Silurian " there 

 was a great change in physical geography. How 

 long a time had elapsed since the Lower Silurian 

 strata had been formed, with their enclosed great 

 sheets of volcanic lava and ash, may be guessed at 

 from the fact that the May Hill conglomerates are 

 composed of the waste fragments of the former ; 

 they had therefore been solidified into such rock as 

 you now see them, and been uplifted from the sea- 

 bottom into coast sections, and it was from their 

 wear-and-tear when in the latter condition that the 

 May Hill conglomerates were formed. Thus does 

 the very structure of many of these deposits indi- 

 cate the immense amount of time which elapsed 

 during their elaboration. It was during the depo- 

 sition of the " Upper Silurian " beds, however, that 

 life was most prolific— was most varied. The sea 

 was aglow with huge coral reefs, around which 

 swarmed sea-lilies, star-fish, mollusca of innumera- 

 ble species, nautili, orthocerata (of whimsical and 



various shapes), and trilobites. The scene was most 

 busy and most animated; the compound corals 

 shone in various colours, and the adjacent sea- 

 bottom was literally a submarine forest of crinoids, 

 or sea-lilies. How abundant these lovely creatures 

 were you may guess from the fact that you can 

 scarcely pick up a fragment of Upper Silurian lime- 

 stone without perceiving some of their detached 

 ossicles, or jointed plates. Iu and out of these 

 waving forests, with the arms of the animals repre- 

 senting branches, the innumerable species of trilo- 

 bites swam, and crawled, and climbed. Every now 

 and then some brightly coloured pecten flittered by 

 like a butterfly. Univalves {Murchisonia and 

 Euomphalus) of delicate ornation and colour, slowly 

 dragged their pretty shells about ; the Cystideans, 

 with their dwarfed stalks, but highly ornamented 

 and sculptured heads, dotted the sea-bottom. Over 

 all the occasional long arms of star-fish wound and 

 unwound ; the delicately beautiful nautilus, of 

 various species, sometimes walked, sometimes filled 

 its air-tube, and mounted to the surface. The 

 whole of Wenlock Edge, in Shropshire, is nothing 

 less than an ancient Silurian coral reef, around 

 which, millions of years ago, all the vital circum- 

 stances I have been attempting to describe took 

 place ! Of all these beautiful coral forms none 

 were so lovely as the "Chain-coral" {Halysites 

 catemdatus). Well does it deserve its name, for 

 even now it appears like some watch-chain of ex- 

 quisite workmanship interfolded in the solid rock ! 

 The largest of these corals was the Favosites poly- 

 morphs. Amidst all should not be forgotten the 

 nests, groups, or even banks of Terebratula, Atrypa, 

 Rhynconella, Spirifera, Producta, Strophomena, and 

 Pentamerus ; all of them belonging to the lowest 

 class of mollusca, then in luxuriant abundance, now 

 waning into extinction. Towards the close of the 

 Upper Silurian period, Vertebrata, in the form of 

 fishes, made their appearance : at first they were 

 few in number and small in size ; but ere long they 

 multiplied amazingly. They had their old feeding 

 and breeding grounds, and along this part of the 

 old sea-bottom their remains were of course most 

 thickly accumulated. Such is the explanation of 

 the Ludlow bone-bed. I am told that off the 

 western coast of Ireland, near Ilockall, such a 

 bone-bed is now actually in course of formation ; so 

 that if it becomes covered over by succeeding de- 

 posits, it may one day present a similar appearance. 

 Of the land plants of this period I cannot say 

 much ; but that the dry land was more or less clad 

 with green, I have not the slightest doubt. What 

 makes me feel so confident about this is that the 

 small spores of club-mosses are to be found fossil- 

 ized in the " bone-bed " I have mentioned. You 

 can only see them with the microscope, but there is 

 no doubt as to what they really are. These spores 

 must have been carried by the land-breezes sea- 



