part 4] PLIOCENE deposits of Cornwall. 355 



yield interesting well-worn quartz-pebbles, quartz-veined ' killas ' 

 pebbles, rounded schorlaceous fragments, and (more rarety) rounded 

 pebbles of cassiterite.^ A few coarser grit-bands are present in tlie 

 red sand, but they are essentially local and discontinuous. 



[b) St. Erth. 



Here again the clay and sand facies are both developed in these 

 deposits, although unfortunately we are no longer able to study 

 the former in situ ; for the old section in the Vicarage pit at 

 St. Erth, in which the fossiliferous clay occurred (see p. 351), we 

 must refer to Prof. P. F. Kendall & P. Gr. Bell's diagram in their 

 paper dealing with the Pliocene fauna of this deposit.^ From 

 the details given it is evident that the section showed a few feet 

 of * Head ' capping about 6 feet of yellow sand overlying the clay ; 

 the latter rested upon a much thicker band of ' fine quartzose 

 sand ' persistent to the base of the series. Unfortunately, the 

 authors of this paper omitted all details as to thickness of these 

 beds ; but, from particulars given by Clement Peid,^ and from 

 the section which it is now possible to measure in the uppermost 

 yellow sand at the Vicarage pit, it would seem that the clay varied 

 from 7 to 8 feet in thickness, and the underlying sand from 10 to 

 12 feet in thickness. The pit now only shows about 5 feet of 

 the uppermost yellow sand. 



The St. Erth sands vary lithologically in much the same manner 

 as those of St. Agnes do : the same yellow, white, and brownish- 

 red facies, with an associated grit-band, are present, and the last- 

 mentioned contains several small pebbles of quartz, killas, green- 

 stone, and schorlaceous material ; this grit-band, although quite 

 conspicuous where it does occur, is non-persistent and of little 

 value as a definite horizon. Other seams of pebbles are scattered 

 promiscuously throughout the red sand ; such pebbles are always 

 well worn and by far the greater percentage consists of quartz. A 

 loamy sand underlying the grit-band is a well-differentiated facies, 

 of a consistency contrasting markedly with the white and yellow 

 sand above ; it constitutes the best moulding-sand from the ]Dit, 

 and is of importance on that account. Current-bedding in this 

 series is not a well-marked feature, although it may be detected 

 in some instances on a small scale ; in this respect, we may note a 

 further similarity to the St. Agnes deposits. On the whole, the 

 St. Erth deposits are of finer texture than those of St. Agnes or 

 St. Keverne, particularly the last-named ; their general lithology 

 suggests deposition in deeper water than in the other cases. 



The lithological character of the deposit alleged to occur on the 

 opposite side of the valley at Lelant Downs, has already been 

 mentioned (p. 351). 



^ ' The Geology of the Country around Newquay ' Mem. Geol. Surv. 1906, 

 p. 64. 



2 Q. J. G. S. vol. xlii (1886) %. 1, p. 202. 



^ ' The Pliocene Deposits of Britain ' Mem. Geol. Surv. 1890, pp. 59 et seqq. 



