227 



the Pecten zones at Aust, Penarth, Watchett, and Uphill, (fee, are 

 composed entirely of hard grey crystalline, and sometimes Pyritic 

 Limestone, with numerous other species crowded into the same bed ; 

 indeed it is remarkable that, compared with other localities, the absence 

 of Lime is a marked feature in the Westbury section.* We now arrive 

 at a singular and interesting bed (No. 14 in section,) most irregularly 

 constructed, and vaiying in conditions, being nodular or septariform, 

 intermittent, or lenticular, yet continuous, and apparently incorporated 

 with the crystalline Limestone band just mentioned, but above it, or at 

 times apparently reposing upon the denuded surface of the grey marls, 

 No. 13. This is the Estheria Zone; and is, I believe, the culminating 

 point of the minute species of Crustacea, giving rise to the name of the 

 bed or zone, and so called from the universal distribution of Estheria 

 minuta on the same horizon thi-ough Great Britain. And, it must be 

 noticed, that no marine forms occur, or are associated with this Crustacean 

 in these creamy marls at Westbury, or in marls of the same age and 

 position, and similarly constructed, at Coombe Hill, Wainlode Cliff, Aust 

 Passage, Pyle Hill, Knowle Hill, and Bedminster Down, near Bristol; 

 at all of which places, as well as sections in Warwickshire, these white 

 marls, containing Estheria minuta, occupy the same relative position. 



At Westbury, this bed forms a conspicuous band in the cliff, from its 

 whiteness and irregular character, and is from 4 to 18 inches in thickness. 

 In structure it resembles hard grey Chalk, or white smooth earthy Lime- 

 stone, and the Estherise occur in nests or nodules, which lie in the many 

 laminations of the bed, and the whole on the irregular or eroded shelly 

 crystalline Limestone above mentioned, t The equivalent of this bed 

 and its Estheriae in cream colored marl 4 inches thick, and other beds 

 above, I obserA'ed last summer, when constructing my section at Coombe 

 HUl, the Estheria marl there resting upon 15 feet of dark brown 

 Shales, both of vliich seem to have escaped the observations of former 

 iuvestigatore, and, which adds considerable interest to the Coombe Hill 

 Section, increasing the thickness of the Rhsetic beds there, to 35 instead 

 of 15 feet, — i.e. 20 feet moi'e are added to the upper black Shales and 

 Estheria group ; or, if we take in (which we miist do) the gi'ey, and red, 



* These facts will clearly appear on the completion of the sheets of comparative 

 vertical sections now being drawn and prepared by Mr. Bristow and myself, illus- 

 trating the Rhjetic series of the West of England. 



\ The importance of this group of Cnistacea (Limnadidae) in time, and of this 

 species in particular, is admirablj' detailed by Professor Rtpert Joxes in the 

 Palaeontographical Soc. vol. for 1860, pp. 42 — 78. 



