Ch. XXVIL] absence of FISH IN LOWER SILURIAN. 58? 



flourished for centuries. In the summer of 1850, Prof. E. Forbes and 

 Mr. McAndrew dredo-ed the bed of the British seas from the Isle of 

 Portland to the Land's End in Cornwall, and thence again to Shet- 

 land, recording and tabulating the numbers of the various organic 

 bodies brought up by them in the course of 140 distinct dredgings, 

 made at different distances from the shore, some a quarter of a mile, 

 others forty miles distant. The list of species of marine invertebrate 

 animals, whether Radiata, Mollusca, or Articulata, was very great, and 

 the number of individuals enormous ; but the only instances of verte- 

 brate animals consisted of a few ear-bones, and two or three vertebrae 

 of fish, in all not above six relics. 



It is still more extraordinary that Mr. McAndrew should have 

 dredged the great " Ling Banks " or cod-fishery grounds off the 

 Shetland Islands for shells without obtaining the bones or teeth of 

 any dead fish, although he sometimes drew up live fish from the 

 mud. This is the more singular because there are some areas where 

 recent fish-bones occur in the same northern seas in profusion, as I 

 have shown in the " Principles of Geology " (see Index, " Vidal ") ; 

 two bone-beds having been discovered by British hydrographers, one 

 in the Irish Sea, and the other in the sea near the Faroe Isles, the 

 first of them two, and the other three and a half miles in length, 

 where the lead brings up everywhere the vertebras of fish from vari- 

 ous depths between 45 to 235 fathoms. These may be compared to 

 the Upper Ludlow bone-bed ; and on the floor of the ocean of our 

 times, as on that of the Silurian epoch, there are other wide spaces 

 where no bones are imbedded in mud or saucl. 



It may be true, though it sounds somewhat like a paradox, that 

 fish leave behind them no memorials of their presence in places 

 where they swarm and multiply freely ; whereas currents may drift 

 their bones in great numbers to regions wholly destitute of living 

 fish. Such a state of things would be quite analogous to what takes 

 place on the habitable land, where, instead of the surface becomino- 

 encumbered with heaps of skeletons of quadrupeds, birds, and land- 

 reptiles, all solid bony substances are removed after death by chemi- 

 cal processes, or by the digestive powers of predaceous beasts ; so 

 that, if at some future period a geologist should seek for monuments 

 of the former existence of such creatures, he must look anywhere 

 rather than in the area where they flourished. He must search for 

 them in spots which were covered at the time with water, and to 

 which some bones or carcases may have been occasionally carried by 

 floods and permanently buried in sediment. 



In the annexed Table, a few dates are set before the reader of the 

 discovery of different classes of animals in ancient rocks, to enable 

 him to perceive at a glance how gradual has been our progress in 

 tracing back the signs of vertebrata to formations of high antiquity. 

 Such facts may be useful in warning us not to assume too hastily 

 that the point which our retrospect may have reached at the present 



