116 Mr. J. Lycett on the Fossil Coixchology 



werci in process of deposition, a molluscous class (the carnivorous 

 Trachelipods), which in our present seas perform the office of 

 keeping down within due limits the other molluscous races, did 

 not then exist, or that they were extremely few, and that it was 

 only on the extirpation of those extensive genera of Cephalopods, 

 the Ammonites and Belemnites, at the commencement of the 

 tertiary epoch, that the carnivorous Trachelipods made their ap- 

 pearance. Living in a district distinguished by a great profu- 

 sion of molluscous remains, a large proportion of which are abso- 

 lutely unknown to science, a favourable opportunity for testing 

 the correctness of the foregoing theory was presented to me, 

 more especially as these remains occur in an unusually good 

 state of preservation, extending in some instances even to the 

 original colours of the univalves, the hinges of the bivalves, and 

 the external ligament of the hinge in the latter shells. Before 

 however stating the results of this inquiry, a veiy brief sketch of 

 the physical and geological characters of the district may not be 

 unacceptable to the members. 



A circle having a radius of only four miles, with the town of 

 Minchinhampton in the centre, will comprise the whole district 

 to which these fossils refer. The Bath Oolite, or Compound 

 Great Oolite as it is now termed by geologists, is the uppermost 

 formation ; its continuity is however broken by two gi'eat valleys 

 of denudation, the vales of Brimscomb and Woodchester, which, 

 with their numerous lateral ramifications, have cut through the 

 whole series of rocks from the upper part of the Great Oolite to 

 the middle of the lias inclusive, having a mean depth of 500 

 feet, thereby producing a combination of circumstances eminently 

 favourable for exposing the useful beds of stone and conveying 

 it by water-carriage. 



The divisions of the Compound Great Oolite are. Great Oolite 

 and Fuller's Earth, the former having a thickness of 130 and 

 the latter of 70 feet. At some few localities the base of the Great 

 Oolite has one or two beds of true Stonesfield slate associated 

 with brown marls. In this respect however, as in the mineral 

 character of the formation generally, the greatest variety and 

 uncertainty exist ; opposite sides of the same quarry will often 

 exhibit such a change ; thus an oolitic and shelly limestone will 

 pass into a barren sandstone. Keeping this fact in view, a con- 

 siderable latitude must be allowed in the following arrangement, 

 which is given only as a general and approximate view of the 

 whole series of beds. The Great Oolite proper may be con- 

 veniently subdivided into three series of beds, an upper and 

 lower fossil iferous, often serviceable for building purposes, and 

 a middle, more ban-en and unserviceable. Beginning with the 

 uppermost, or those which immediately underlie the Bradford 



