86 Mr. Charles worth on the Crag-formation 



the known habit of particular species congregating in distinct 

 localities, those portions of the stratum may have been de- 

 stroyed, in which these shells, perhaps, constituted the princi- 

 pal part of its organic remains. 



" I am inclined to think the whole of the upper stratum has 

 been produced from the ruin of the lower. I herewith give 

 you a summary of my cabinet, as far as relates to the Testacea: 

 the classes Polypi, Radiaria, and Crustacea, of which nu- 

 merous remains are found, cannot at present be enumerated. 

 Many of the shells from the upper crag have long been 

 figured by Sowerby: I have collected 235 species; two thirds 

 of these are also met with in the lower. The following is the 

 joint production of the two strata ; and from the labour I have 

 bestowed upon the subject, unless some new localities be dis- 

 covered, I think the list will not for some years be much ex- 

 tended. 



Annulata J 3^ 



Cirripeda 11 i 



Conchifera 189 f s P ecies ' 



Mollusca 257j 



" Making a total of 450 species. 



" The last number includes 50 species of minute cephalo- 

 podous mollusca of the order Foraminifer a, D'Orbigny, which 

 exclusively belong to the lower stratum, and which I think 

 I am entitled to the claim of bringing into notice*/* 



It appears by this statement that of 450 species collected 

 by Mr. Wood, about 80 are peculiar to the red crag, upwards 

 of 200 peculiar to the coralline, and the remaining 150 com- 

 mon to the two formations. 



One or two writers in alluding to the crag have observed, 

 that it assumes a remarkable change in character at Aid- 

 borough, the eastern boundary of the formation. Mr. R. C. 

 Taylor particularly remarks this circumstance, describing this 

 part of the stratum as a " soft porous rock, mixed with in- 

 teresting varieties of corals and sponges." Aldborough, how- 

 ever, does not afford so favourable a field for the researches 

 of the geologist as Sudbourne and Orford, two parishes on 

 the estate of the Marquis of Hertford, and about six miles 

 from the former locality. Here the quarries are very nu- 

 merous, but, with the exception of that described in a former 

 part of this paper, they afford only a small proportion of tes- 



* This discovery of the minute cephalopodous mollusca, by Mr. Wood, 

 is a most interesting one. Mr. Wetherell ofHighgate (whose extensive 

 and valuable collection of fossils is well known,) showed me several species 

 which he had procured from the London clay. 



