554 H. HICKS ON THE DEPOSITION OF THE 



rate than would keep pace with the accumulations. This is partly 

 due to the slow arid regular depression, and partly to the increased 

 area exposed to the action of the waves by the spreading of the 

 water during the Menevian epoch. Doubtless also much loose ma- 

 terial was washed down from the continents as they were depressed ; 

 and this was being continually carried out from the shores and 

 spread over the accumulations, so filling up areas which otherwise 

 would have been covered by deeper water. The next rather sudden 

 depression was that which took place at the commencement of the 

 Tremadoc epoch ; and it was at this period that the western and 

 southern parts of Russia became submerged ; for we do not find any 

 beds there of older date than our Arenig or Llandeilo, and these 

 seem to rest directly on the old prse-Cambrian land. During the 

 depression, which extended over the Tremadoc, Arenig, and Llandeilo 

 periods, moderately deep water covered the western areas ; and the 

 accumulations are consequently of a fine muddy character, unless 

 when under the influence of tidal currents, or, as at the close of the 

 Arenig, of volcanic disturbances. The land at this time under the 

 immediate influence of wave-action was far removed from these 

 areas; and the deposits therefore were heaped up more slowly, as may 

 be seen in the fine slaty beds in Prance and England. In Wales, a 

 region much disturbed afterwards by volcanic agencies, at least 4000 

 feet of these fine muddy deposits were thrown down before the 

 commencement of volcanic action in that region; and these were 

 formed independently of volcanic products. 



In Russia, in consequence of being near the wave-action and the 

 remaining continental area, which probably did not become sub- 

 merged in parts of Asia until the Devonian epoch, gritty beds were 

 thrown down at this time. 



At the close of the Lower Silurian the sea-bottom was possibly in 

 in some parts raised above sea-level ; but it is evident that in most 

 areas it remained still submerged. The elevation seems to have been 

 chiefly along the line of volcanic action, and was doubtless assisted by 

 movements in the earth's crust, as well as by the spreading of ashes 

 and lavas over the sea-bottom. The volcanoes at first were sub- 

 marine ; and though in some cases they afterwards seem to have 

 heaped up sufficient material to rise above the surface of the water, 

 yet they all became submerged again before the close of the epoch, 

 and conformable sediments are seen to cover them over. The stra- 

 tigraphical evidence therefore strongly favours the view that a 

 gradual depression took place during the whole of the Cambrian 

 and Lower Silurian epochs over the European area, and that the 

 deposits form one complete and natural succession from the base 

 upwards. The evidence derived from a consideration of the faunas 

 is entirely in accordance with this view. In no case do we find 

 any forms but those which must have been marine ; not a single 

 freshwater fossil has yet been found. The first fauna of which we 

 have any knowledge occurs in the beds furthest to the west, and 

 there in earlier beds than any which occur in the regions more to the 

 east ; and though the forms which make up this fauna belong to 



