84 



THE FAR PAST. 



pebbles, and coral-growths of seas and estuaries. It is 

 customary for a certain class of geologists to talk of 

 " the deep, turbid, and shoreless seas" of the Silurian 

 epoch, as if the globe was then enveloped by one dreary 

 monotony of ocean. Do such generalisers ever for a mo- 

 ment think that such a vast thickness of sediments could 

 never have been produced without the existence of broad 

 lands from which they were transported by rivers, or of 

 sea-shores from which they were abraded by waves and 

 tidal currents 1 Could conglomerates be formed without 

 wave-exposed beaches, sands without open sea-shores, or 

 could shells that are truly littoral, and corals that nourish 

 only from twenty to sixty fathoms, have existed without 

 water of limited depth for their development ? The eye of 

 the trilobite would have been useless in a turbid ocean ; a 

 turbid ocean w r ould have been death to the growth of corals ; 

 worm-burrowed, ripple-marked, and rain-pitted sandstones 

 could have been formed only on shores exposed to the 

 alternate ebb and flow of the tide ; and conglomerates are 

 merely the broken-down and water- worn fragments of an 

 older rocky shore. In fine, there is not a single feature in 

 the rocks of the Silurian period which might not take place 

 in the ocean of our own day. The existence of deeper and 

 shallower seas of waves, currents, tides of lands, shores, 

 and rivers of sunlight, and rains, and winds are as clearly 

 impressed on its strata as they are upon those of every 

 other geological epoch. It differs alone in the geographical 

 distribution of its sea and land the greater insularity, 

 perhaps, of the land-masses their consequent climatology 

 and the specific characters of its plants and animals ; though, 

 knowing the wide extent of its deposits (and they occur 

 alike in the continents of the Old and New World, in the 

 northern and in the southern hemisphere), geology is not 

 yet in a position to map with accuracy the geography of the 



