Geology of the Bermudas. 



391 



These shells are light in weight, bleached, brittle, and have lost their 

 animal membrane seemingly, and are adherent slightly to the tongue. 

 The caves owe their existence to the abundant rainfall during 

 Pliocene and later times, and have been formed by solution and by 

 underground streams very much as the caves of the Causse district in 

 France and those of Derbyshire have been dissolved out. It will be 

 seen in the later part of this paper that the sea can have had little 

 or no part in their causation except where the caves are situated on 

 the shore, and in this case they have apparently only been irrupted, 

 not formed, by the sea. The sea, as at Cathedral Rocks in Somerset 

 parish, has rather destroyed and opened out cavities which were 

 previously existing. 



FlG. 4. Pcecilozonites Bermudensis, var. zonatus, Verrill, from Castle Harbour 

 Cliff. (Specimens from the later Paget rock formation ; in the brightness of 

 their colour and state of preservation are comparable to the H. nemoralis 

 of the Abbott Fissure at Ightham.) Drawn by G. M. Woodward. 



It is said that for crystallization to take place there must not only 

 be abundance of water supersaturated with calcic carbonate, but also 

 rapid evaporation. This is probably true. But it is probably true also 

 that, given ' efficient drainage, the matter in solution is deposited by 

 the arrest of the running and percolating water, and that the calcic 

 material may be precipitated quite as much by such arrest as by 

 evaporation. It would be difficult otherwise to account for the thick 

 deposits in the immense caves of Kentucky, Belgium, Mallorca, and 

 elsewhere. For though evaporation can never be very great in the 

 cool depths of such caves, the enormous deposition of stalactite and 

 stalagmite is a fact everywhere patent in them. 



At the top of the Walsingham formation there is a layer of red soil 

 (see Text-fig. 1). This is due seemingly to the solution of the overlying 

 shell-sand, just as the red clay (on the Chalk plateau) is partly due to 

 the dissolution of the Chalk. In Bermuda the red clay must be wholly 

 a dissolution product. The shell-sand which makes up the great mass 

 of these aeolian sands is not all soluble, and some of the material is 

 left after the calcic material has been dissolved out. This residuum is 

 taken to represent the remains of 150 feet of shell-sand for every foot 



