550 MK. E. WETHERED ON THE INFERIOR 



31. The Inferior Oolite of the Cotteswold Hills, with Special 

 Reference to its Microscopical Structure. By Edward 

 Wethered, Esq., F.G.S., F.C.S., F.R.M.S. (Head May 6, 1891.) 



[Plate XX.] 



Contents. 



Page 



Part I. — The General Structure. 



(a) Introduction 550 



(b) The Transition Beds 550 



(c) The Pea-Grit Series 552 



(d) The Building Freestones ... 557 



(e) The Eagstones 558 



Part II. — Insoluble Residues. 



(a) Details of Residues in the Beds referred to in Part 1 559 



(b) General Summary of the Residues 564 



(c) Origin of the Residues 565 



(d) The quantity of Residue and size of the Quartz-grains 566 



Part I. — The General Structure. 

 (a) Introduction. 



The main divisions of the Inferior Oolite in the Cotteswold Hills 

 are known to geologists who have made a study of Jurassic rocks, 

 but to those who have not done so and to foreigners they may be 

 less familiar. In order, therefore, that my remarks may be the 

 more easily understood, I indicate the following main divisions which 

 I propose to adopt, deferring my explanations of them till later on. 

 They are given in descending order : — 



Ragstones. 



Upper Freestones. 



Oolite Marl. 



Lower Freestones. 



Pea Gi'it. 



Transition Beds, resting on the Upper Lias. 



(b) The Transition Beds. 



Position and General Structure. — There has been considerable 

 discussion among geologists as to where the line is to be drawn 

 between the Inferior Oolite and the Upper Lias. To give even a 

 summary of the controversy would take up considerable space and 

 tend to divert the reader's attention from the primary object of this 

 paper. I will, therefore, only mention the views of two geologists 

 who may be said to represent the respective contentions. The late 

 Dr. Wright, F.Il.S., referring to the zone of Harj^oceras opalinum^ 

 said * : " This zone was formerly grouped with the Cephalopoda-bed 

 of Frocester ; but, as it contains some species which are limited to 



* 'Monograph of the Lias Ammonites,' Pal. Soe. vol. xxxiii. (1879) p. 148. 



