70 THE SILUKIAN PERIOD. CHAP. 



of the sea-bed in this region ; a subsidence which brought currents 

 into the sea, most of them loaded with sandy, rarely conglomeratic 

 sediments. 



Three pauses in the ' depression' are marked by the limestones 

 of Woolhope, Wenlock, and Aymestry. Each of these pauses was 

 favourable to the growth of coral, and indeed large portions of the 

 limestones are in places composed of these radiated structures. 



Slaty cleavage is unknown in the whole district, though it 

 occurs further south. There is little sign of oceanic disturbance 

 in the whole mass of strata, which is above 3000 feet thick ; but 

 few traces occur even of strong ripple mark ; and the appearances 

 suggest a limited sea-basin, guarded from violent stonns, and free 

 from any considerable influx of fresh water. It might be about 

 the quiet end of a sea-basin, much extended to the north and west, 

 and there exposed to ruder wave-action and greater vertical move- 

 ment. There is no reason for supposing the strata to have been 

 deposited in very deep water. 



Excepting the black shale of the Cambrian series and the purple 

 beds which rest upon it, all the strata of Malvern are of grey, or 

 pale-bluish colour, when examined at a considerable depth below 

 the surface, as in the Malvern Tunnel. Near the surface these 

 tints, indicative of protoxide or silicate of iron, become yellow 

 or brownish, the oxide having passed to the condition of proto- 

 carbonate. The limestones have been examined as to their basis, 

 in hope of finding foraminifera and small fragments of organic 

 tissues, especially in the occasionally pisolitic beds of the Wenlock 

 series. Only one foraminifer has occurred to my observation, viz. 

 Endothyra Bowmanni, the beautiful spiral shell which I described 

 from the mountain limestone some twenty years ago. I have seen 

 traces of it in the Upper Silurian limestone of Russia. 



In the following Table the Cambrian and Silurian strata of the 

 Malvern region appear in their relative thicknesses : 



