Mr. Webster on the Strata lying over the Chalk. 243 



The grounds upon which this supposition is made, is the obser- 

 vation that the recent analogues of most of these fossils are now in- 

 habitants of the torrid zone. The extreme delicacy however of 

 most of these shells, as well as their perfect preservation (as Mr. 

 Parkinson has already observed,) precludes entirely the possibility of 

 their having been brought from distant places, and they serve merely 

 to shew that this part of the globe must be very different, relatively 

 to such species of animals, from what it was at the period of their 

 entombment. 



In some beds of pebbles and gravel fossil shells are very numerous, 

 as in those of Woolwich, Harwich, &c. and with these alternate fre- 

 quently beds of clay and sand, containing shells regularly distributed, 

 entire, and apparently undisturbed. Of these shells Mr. Parkinson 

 observes, some belong to species now only found in distant seas, and 

 others appear " not to differ specifically, as far as their altered state 

 " will allow of determining, from the recent shells of the neigh- 

 " bouring sea," 



But granting, as we must, that the formation of pebbles has taken 

 place at different periods, it must be extremely difficult, and per- 

 haps impossible in all cases, to distinguish whether they are now to 

 be seen in the places where they were at first deposited, or whether 

 they may not have repeatedly been moved. 



In many beds of gravel delicate shells are so abundant that the 

 cause which placed them there could not have been very violent ;. 

 whilst others are found totally destitute of organic remains, except 

 such as are impressed upon the substance of the pebbles themselves. 

 Among the latter may be enumerated, pectines, anomise, the inte- 

 rior casts of echini, and impressions of the spines and plates ; zoo- 

 phytes of unknown genera, some resembling alcyonia, are also fre- 

 quent. It does not appear certain whether all these may not have 



2 H 2 



