No Dawn of Organic Life in the Silurians. 7 



as little proof of a restless and chaotic state of the planet, 

 as if earthquakes were more frequent and violent, or the 

 waves loftier, or the marine currents swifter than at pre- 

 sent. The corals and crinoids imply pure, clear, and many 

 of them tranquil water, the pebbles are not larger than 

 those of succeeding epochs, and the ripple-marked sands at 

 the bottom of the series, as seen for example in the Potsdam 

 sandstone of Vermont, precisely resemble those of a modern 

 beach. The doctrine of intermittent paroxysms, with long 

 intervening periods of repose, is certainly preferable to a 

 theory of chronic turbulence, for those who despair of ex- 

 plaining all ancient disturbances of the earth's crust by the 

 cumulative effect of prolonged movements, or the indefinite 

 repetition of shocks of minor violence. But I must refer 

 you for my views on this subject to my Anniversary Address 

 of last year. 



Some eminent naturalists have assumed that the earliest 

 fauna was exclusively marine, because we have not yet found 

 a single Silurian helix, insect, bird, or terrestrial reptile or 

 mammifer. But if any one wishes to convince himself of 

 the rashness and unsoundness of such generalizations, he 

 need only study the results of a recent dredging expedition, 

 conducted by Prof. E. Forbes, not in seas of considerable 

 depth and somewhat remote from land, like those in which 

 the greater part of the Silurian strata were deposited, but 

 near our coast. 



I allude to the observations laid before the British As- 

 sociation, at Edinburgh, in 1850, by Messrs Forbes and 

 Mac Andrew, who, in the summer of that year, explored the 

 bed of the British seas from the Isle of Portland to the 

 Land's End, and thence again to Shetland. They have re- 

 corded and tabulated the numbers of the various organic 

 bodies, obtained by them in 140 distinct dredgings, made at 

 different distances from the shore, varying from a quarter 

 of a mile to forty miles. The list of marine invertebrate 

 animals, both radiata, mollusca, and articulata, is by no 

 means inconsiderable, but very few traces of any vertebrate 

 animal were found. When these occurred (in five or six 

 cases only) they were limited to fish, consisting of a few 



