vi INTRODUCTION. 



has been but inconsiderable ; these latter belong chiefly to Ancliff, 1 and to the vicinity of 

 Scarborough. The parallelism of the deposits at the two former places would appear 

 to be well ascertained, but with respect to the rocks which are so extensively exposed 

 upon the coast of Yorkshire, although the evidence of geological position appears to 

 be satisfactorily determined, they possess but few mineral features which serve to connect 

 them with their supposed equivalents in Gloucestershire, Wiltshire, and Somersetshire ; 

 they constitute a great carboniferous deposit of the Oolitic period, abounding with land 

 plants, and containing intercalated bands or thin beds of dark gray argillaceous shales, 

 limestones, and sandstones, containing marine shells, of which only a minority of species 

 have been identified in other localities. The evidence afforded by the few species of 

 univalves which have been forwarded to the authors from Scarborough, through the 

 kindness of Mr. Bean, though not conclusive, tends rather to assimilate them with the 

 Inferior Oolite ; and it will be perceived on consulting the table of species at the end of 

 the Monograph, that of the twenty-one Yorkshire species, none have been identified with 

 Great Oolite shells of Minchinhampton or Ancliff, but that seven agree specifically with 

 Inferior Oolite shells of the Cotteswold hills. The Yorkshire deposits to which these 

 remarks refer constitute the entire series of plant-bearing beds numbered 11, 12, and 13 

 in Phillips's ' Geology of Yorkshire,' reposing on No. 14, or the Dogger, which is proved by 

 its fossils to be the equivalent of the Inferior Oolite, or at least to a portion of that 

 formation. Admitting, therefore, the parallelism of the deposits containing somewhat 

 distinct Faunas, in the north-eastern and south-western parts of the present area of 

 England, we are naturally led to infer, either that the physical conditions might be favor- 

 able to the continuance of species in one locality, or that species characteristic of an older 

 deposit, in a more distant region, may have migrated and lived on during the formation of 

 a newer deposit in another, the conditions having become unfavorable to the perpetuity 

 of their development in the latter deposit over the original region whence they had 

 migrated. 3 



For the above-mentioned reasons, it has been deemed desirable to separate the 



1 The section at Ancliff, near Bradford, is as follows : 



Rubble . 5 feet. . . Abounding with Polyparia. 



Soft Oolite 15 . . This is the bed celebrated for the Ancliff fossils. 



Clay . 1 . . Containing small sponges, and many fragments of shells. 



Rag . 6J . . Very coarsely Oolitic. 



Soft Oolite 5 



From Mr. Lonsdale's interesting memoir, " On the Oolitic District of Bath," in the 'Geol. Trans.,' vol. iii, 

 p. - _';i2, in which many other sections of the Great Oolite are given, and the range of the deposit in that 

 neighbourhood is accurately traced. 



2 Unfortunately the entire character of the fauna of the Great Oolite in the centre of England is not 

 well ascertained, nor is the range and extent, southerly, of the fluvio-marine conditions of the Yorkshire 

 Oolite accurately determined. As bearing on this point, the reader is referred to a paper by Captain 

 L. L. B. Ibbetson arid Mr. Morris, "On the Geology of Stamford" ('Brit. Assoc. Rep.,' 1847, p. 127). 

 The subject of migration of species, during the Oolitic epoch, is ably treated in a valuable memoir by 

 M. Gressly, 'Observations Geologiques sur la Jura Soleurois.' 



