A MONOGRAPH 



OP THE 



MOLLUSCA FROM THE GREAT OOLITE. 



GENERAL GEOLOGICAL REMARKS. 



THE Minchinhampton district of the Great Oolite has produced by far the greater 

 number of our illustrative specimens ; and as the formation at that locality exhibits features 

 of a very varied as well as comprehensive character, we may be excused for entering 

 somewhat more into detail in our remarks upon it. The Great Oolite in this portion of 

 Gloucestershire constitutes the uppermost rock of the Cotteswold Hills ; it everywhere 

 overlies the Fullers-earth, which, in turn, reposes upon the uppermost beds of the Inferior 

 Oolite; there is, therefore, a regular unbroken sequence of the Oolite rocks exposed on 

 the flanks of the various deep valleys of denudation which pervade the district. The 

 physical features of the district are strongly marked ; the larger valleys have a mean depth 

 of about 500 feet, and exhibit what can scarcely be met with in any other part of England ; 

 a single unbroken declivity comprising the Great Oolite, Fullers-earth, Inferior Oolite, and 

 upper portion of the Lias. The Inferior Oolite at these escarpments has a thickness of about 

 230 feet, the Fullers-earth of 70 feet, and the different beds of Great Oolite of 120 feet ; but 

 of these latter, only about the lower 40 feet anywhere approach to the brow of the escarp- 

 ments. The narrow and deep vale of Chalford, with its lateral branches, intersects the 

 strike of the Great Oolite, and divides the fossiliferous portion of the district into two parts ; 

 another and wider valley, further south, likewise intersects the strike of the formation. In 

 this are situated the villages of Woodchester, Hailsworth, and Avening ; but here the 

 amount of denudation, horizontally, has been more extensive ; and as the Great Oolite is 

 likewise much less fossiliferous, it need only be adverted to as supplying many additional 

 positions, where the rock can conveniently be quarried by open-work excavations. It will, 

 therefore, be perceived that the natural features of the district eminently conduce to the 

 study of its organic remains. 



