1857.J GODWIN-AUSTEN BOULDER IN CHALK. 261 



mentary, as regards the Testacea more particularly ; and taken alto- 

 gether they imply a drifting power, whereas the nature of the sea- 

 beds indicates only conditions of tranquil deposition. Recognizable 

 forms from the Chalk bear so small a proportion to its mass — the 

 formation nowhere throughout its vast thickness presents old sea- 

 floors over which a fauna lived* — that I am disposed to consider the 

 greater part of the animal remains which it contains as having been 

 raised off shallower zones, floated away, and scattered outwards over 

 the deeper ones. 



This view of the Chalk-deposit — namely, that all the larger 

 materials which it contains, whether organic or inorganic, belong to 

 a higher sea-zone — is one which admits of a great amount of illus- 

 tration, and deserves separate treatment. It may be sufficient for 

 the purpose for which the view is here introduced, to state that all 

 those forms of Bryozoa which, when living, are fixed at the base 

 only, such as Idmonea, Pustulopora, Desmeopora, and many others, 

 all occur detached in the body of the Chalk. This is also well seen 

 with respect to the Anthozoa : the examination of a large collection 

 of Monocarya centralis showed me that they all had been broken 

 off before they were imbedded. 



With respect to the zone from which the Chalk forms have been 

 mainly derived, it is sufficient that it should have been a higher one, 

 where the accumulation of mineral matter was necessarily very dif- 

 ferent to what it was at extreme depths. I will therefore only call 

 attention to a few Chalk forms, and which also belong to sand- 

 deposits usually considered older than the Chalk : — 



Stellaster elegans, Forbes. In Chalk. Sussex. In sands below 

 the Chalk at Folkestone, and in the sands of Blackdown. 



Serpula plexus. Chalk, and abundant in the Blackdown and 

 Haldon sands. 



Pecten cequicostatus. Chalk, and abundant in the Blackdown and 

 Haldon sands. 



Plagiostoma parallelum. Greensand, Gault, Chalk. 



Considering the poorness of the White Chalk fauna, the proportion 

 of bivalved Mollusca having a byssus is remarkable. Such shells are 

 now widely distributed by floating weed. 



The occasional occurrence of large dead shells of Dolium or Cas- 

 sidaria, of which a single specimen is as yet recorded from our White 

 Chalk, requires for its explanation an agency at least equal to the 

 transport of ordinary shingle. The species seems to be identical 

 with one from the cretaceous sands of Mans, where it is scarce. 

 Dolium would not belong to such a zone ; but the animal has the 

 power of swimming by inflating its disk, and in this way it may 

 occasionally be floated away from the marginal sea-line, and so perish, 

 and sink in deeper water. The form Dolium evidently belongs to 



* The occurrence of a large block of Coral in the White Chalk caused me to 

 form at one time a different opinion. I have now no doubt but that it was a 

 transported mass from some distant reef. Proc. Geol. Soc. vol. iv. p. 169. 



