219 



Dr. Wright, of Cheltenham, in I860,* wrote and conimimicated an 

 able paper upon these beds, and theii- development in Gloucestershire and 

 Somersetshire, adopting for them the term "Avicula contorta Zone," a name 

 first given to this series of shales and marls in the north of Ireland by 

 Colonel PoRTLOCK, t in 1843, and -which contain in abundance, this 

 peculiar, and in that age cosmopolitan, shell, Avicula contorta, thus 

 specifically named by Col. Portlock from its contorted or twisted form. J 



Mr. Charles Moore, of Bath, in the year 18G1,§ wrote a special 

 paper iipon the Avicula. contorta Zone, taking exception to certain •views 

 of Dr. Wright, relative to the true position of the White Lias, in con- 

 nection with, and bearing upon, the classification of this gi-oup. This 

 paper of Mr. Moore's contains good and characteristic figures of the 

 species found in the Avicula contorta or Rhcetic beds in this country. 



The complete history and synonymy of this thinly-developed, yet 

 important series of deposits, it is not my intention to enter upon, my 

 chief object being to give a description of the Garden Cliff, or Westbuiy 

 section, correlating it generally, or in particular instances with others, 

 when necessary, in Gloucestershire or adjacent counties. 



The whole valley of the Severn abounds in features of high Geological 

 interest, both to the Physicist and Palaeontologist, and I know no portion 

 of England where such varied phenomena may be studied ; — where cause 

 and effect, and the ancient and modern physical history of western 

 England, if not Europe, maybe more clearly observed; — where the relations 

 of sea and land, and the grand phenomena of denudation through past and 

 successive epochs can be better investigated- and understood : for the 

 Cotteswolds yield not to the distant, far-famed Jiira, either in physical 

 structure or natui-al grandeur; every feature in that extensive rano'e 

 being duplicated and typified in the boldly scarjied oolitic hills that border 

 the Severn and its extended plain, and which then trend through the 

 middle of England, and lose themselves on the coast of Yorkshire, under 

 the waters of the German Ocean. 



It is in the Severn valley, and at several points, viz., Wainlode Cliff, 

 Aust Passage, andWestbury, that these Rh^tic beds occur, or ai-e exposed: 

 and at the same level, though remotely situated inland, but still exhibiting 

 the same physical features, are the fine sections of Patchway and Saltford 



* Wkight, Quarterly Journal Geo!. Society, vol. xvi., 1860, p. 374. 

 t FoRTLOCK, Report on Geology of Londonderry, 1843, pp. 126, 127. 

 + Gervillia striocurva, (Que>-stedt. ) 



§ Moore, Quarterly Journal Geol. Society, 1861, p. 48.3.,. PL 15, 16, on the 

 Zones of the Lower Lias, and A vicula contorta Zone. 



