vi.] THE SLATES OX THE EOOF. 129 



known, only to be found in the north-west highlands 

 of Scotland, and in the island of Lewis, which consists 

 entirely of them. And it is to be remembered, as a 

 proof of their inconceivable antiquity, that they have 

 been upheaved and shifted long before the Cambrian 

 rocks were laid down " un conformably " on their worn 

 and broken edges. 



Above the " Cambrian " slates whether the lower 

 and older ones of Penrhyn and Llanberris, which are 

 the same one slate mountain being worked at both 

 sides in two opposite valleys or the upper and newer 

 slates of Trenmdoc, lie other and newer slate-bearing 

 beds of inferior quality, and belonging to a yet newer 

 world, the " Silurian/' To them belong the Llandeilo 

 flags and slates of Wales, and the Skiddaw slates of 

 Cumberland, amid beds abounding in extinct fossil 

 forms. Fossil shells are found, it is true, in the upper 

 Cambrian beds. In the lower they have all but dis- 

 appeared. Whether their traces have been obliterated 

 by heat and pressure, and chemical action, during long 

 ages ; or whether, in these lower beds, we are actually 

 reaching that " Primordial Zone " conceived of by 

 M. Barrande, namely, rocks which existed before living 

 things had begun to people this planet, is a question 

 not yet answered. I believe the former theory to be 

 the true one. That there was life, in the sea at least, 

 even before the oldest Cambrian rocks were laid down, 

 is proved by the discovery of the now famous fossil, 

 the Eozoon, in the Laurentian limestones, which seemo 

 to have grown layer after layer, and to have formed 

 reefs of limestone as do the living coral- building 

 polypes. We know no more as yet. But all that we 

 do know points downwards, downwards still, warning 



so. K 



