Considerations connected with the Glacier Theory. 47 



of the Hils-clay and Neocomian strata, as the lowest members 

 of the chalk ; the former is, accordmg to Rcemer's recent in- 

 vestigations, essentially a portion of the chalk {Speeton clay), 

 but contains in Hanover Exogyra spiralis. Pec ten lens, Tere- 

 bratula perovalis, Serpula volulAlis, and Cellepora orbiculata, 

 in common with the Coral-rag and Portland limestone; there- 

 fore a larger number of species than are common to the lower 

 oolite and Oxford clay, &c.* Although Roemer, in his new 

 treatise on the chalk, does not enumerate these species (with 

 the exception of the Terebratula), or forms new species for 

 the individuals occurring in the Hils-clay, yet, on the other 

 hand, according to Dubois, a much greater mixture of Jura and 

 chalk species occurs in the same formation in the Crimea, 

 where in the chalk, out of 49 species, 16 present themselves in 

 the oolite. According to Fitton,-|- 15 species of the oolite oc- 

 cur in the chalk of the south-east of England, but, in regard to 

 this, it is proper to remark, so far as these are derived from 

 Fuller's-earth, that Rcemerj considers Fuller's-earth as the 

 equivalent of the Hils-clay or Speeton clay. In Yorkshire, 

 Phillips finds that the Knapton and Speeton clays afford, out 

 of 107 species, 99 from the chalk and 8 from the Kimmeridge 

 clay, which latter is there awanting. Montmollin and Alex- 

 ander Brongniart enumerate in the Neocomian strata of the 

 Jura, the former 4 out of 14, and the latter 2, as belonging 

 to the oolite. Miss Bennet mentions, that in Wiltshire, 5 species 

 of the coral- rag occur also in the upper green-sand, but I do" 

 not trust entirely to the determinations. Other common species 

 from various localities are to be found in the work of Goldfuss. 

 Most of these species, and also some detected by himself, are 

 ennumerated by D'Archiac in his list. 



IV. The smallest number of common species has been found 

 in the oolitic and trias, or saliferous series ; and yet in Coburg 

 and Wiirtemberg it is extremely difficult to determine with 



* In the more recent works on the chalk, however, that Exogyra spiralis 

 is regarded as a new species. 



t Observations on the strata below the chalk and Oxford oolite in the 

 south-east of England, 1836. 



X Vei-steineruiiffm dn- No^'ddfxilfchen Kreidff HaBOTer, 1841, p. 132, 



