MONOGRAPH 



FAUNA OF THE COBNBEASH 



INTRODUCTION. 



The rock known in this country as the Cornbrash is reckoned as the uppermost 

 member of one of the subdivisions of the Jurassic rocks which are, as a whole, 

 termed the Lower Oolites. This classification, which is still in vogue in England, 1 

 dates back to 1822, having been founded by Conybeare, 2 who writes as follows in 

 his ' Outlines ' : 



" The system of formations occupying the interval [between the Ironsand and 

 the Red Marl] may be generally described as consisting of a series of oolitic lime- 

 stones, of calcareous sands and sandstone and of argillaceous and argillo -calcareous 

 beds alternating together and generally repeated in the same order, i. e. a formation 

 consisting of many beds of oolitic limestone, resting upon one of calcareo-siliceous 

 sand and that again upon an argillo-calcareous formation. Three of these systems 

 comprehend all the beds. Each is based on an argillo-calcareous formation of 

 much thickness. Hence we may give a hypothetical view of the whole series as 

 divided into the Upper, Middle, and Lower Systems." 



This system is, therefore, founded on local lithology, and is characteristic only 

 in the South-West of England, where it originated. 



On the other hand, Mr. H. B. Woodward, who at the present day holds an 

 unrivalled knowledge of the Cornbrash in its stratigraphical bearings, states 

 definitely that " the Cornbrash belongs to the zone of Ammonites macrocephalus. . . . 

 The zone may be said to extend upwards into the Lower Oxfordian strata." 3 

 Here is indicated a definite connection with the so-called Middle Oolites. This is 

 so clearly the fact and comes out so definitely when the fauna is studied, as will 

 subsequently be seen, that it must not be mistaken for a Lower Jurassic horizon — 

 a view which is only accepted as an " hypothesis " by Conybeare. 



1 See Marr, 'Principles of Stratigraphical Geology,' 1898, p. 230; Watts, 'Geology for 

 Beginners,' 1898, p. 271. 



2 ' Outlines of the Geology of England and Wales,' 1822. 

 8 ' Jurassic Rocks of Britain,' vol. iv, 1894, p. 434. 



