2 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [Apr. 6, 



C. Section from the Cornbrash to the Millepore-bed in Gristhorpe 



Bay, Yorkshire. 



D. Sections in Somerset and Dorset, (1) Glastonbury Tor, (2) Yeovil, 



(3) Henbury, (4) Half-way House, near Yeovil, (5) Bradford- 

 Abbas, Dorsetshire. 

 3. The zone of Ammonites Parhinsoni. 



A. Section at (1) Leckhampton Hill, (2) Eavensgate Hill, (3) Cold 



Comfort, (4) Birdlip Hill, (5) Kodborough Hill. 



B. Sections at Dundry, Bath, Yeovil. 



C. Sections near Bridport. 

 § IV. Conclusion. 



§ I. Introduction. — The researches necessary to determine with 

 accuracy the range and distribution of the Echinodermata in time and 

 space, for my monograph on the Oolitic species of that class, necessi- 

 tated a like inquiry into the history of the Mollusca associated with 

 them in the same beds. This study has led to a closer inquiry into the 

 subdivisions of the Oolitic Rocks in the South of England and on the 

 Yorkshire Coast, with the view of reconciling or explaining certain 

 real or apparent exceptions to the distribution of the species in their 

 different stages. The result of these investigations has been the 

 accumulation of a large quantity of materials, a resume of a portion 

 of which, relating to the Inferior Oolite, I purpose giving in this 

 memoir. 



The study of the Oolitic rocks, during late years, has largely en- 

 gaged the attention of English and Continental geologists ; and 

 the united labours of so many competent observers in different lands 

 have brought to light many new and important facts, which have 

 shown how much still remains to be done to complete the history of 

 the Jurassic formation. 



Nor are the results of such investigations limited to a knowledge 

 of these formations only ; for a more accurate examination of the 

 stratigraphical conditions under which the Jurassic rocks were de- 

 posited, and a more critical acquaintance with the specific distinc- 

 tions of their different faunas, will enable palseontologists to apply 

 the knowledge thus acquired to the solution of other problems in 

 geology. Eor in many respects the Jurassic series, as developed in 

 England, affords a better field for accurate investigation than any 

 other system of stratified rocks, inasmuch as its various stages and 

 their stratigraphical sequence, taken as a whole, are more complete, 

 more regular, and better exposed ; the different faunas, likewise, of 

 their various subdivisions have not only been collected with care, but 

 separate monographs on different classes of the Invertebrata have 

 been published by the Palseontographical Society : — on Corals, by 

 Professor Milne -Edwards and M. J. Haime ; on Brachiopoda, by 

 Mr. Davidson ; on the Mollusca of the Great Oolite, by Professor 

 Morris and Mr. Lycett; on the Echinodermata, by myself; to 

 which may be added the Description of the Fossil Insects of the 

 Secondary Rocks, by the Rev. P. B. Brodie. The small number of 

 palaeontologists, who practically study the distribution of species in 

 time, compared with the large number of geologists, who delight in 

 wider and more superficial studies, has led to misunderstandings 

 between these two classes of observers, injurious to the progress of 



