326 Itejjorts and Proceedings — Geological Society of London. 



plateau-like tract extending from the Castell Yalley to the Tstwyth 

 Valley. 



The stratigraphical succession is demonstrated by a series of sections 

 and traverses across various parts of the district, and lists of fossils 

 (mainly graptolites) collected from the various zones are given. The 

 palseontological evidence is in entire accord with the stratigraphical 

 evidence. 



The structure shows many points of interest, and is clearly brought 

 out by the mapping. Three types are dealt with — ( 1 ) folding, 

 (2) strike - faulting, and (3) normal faulting; but the first is 

 predominant. 



The rocks are folded into a primary anticlinal fold or anticlinorium, 

 with a southerly ' pitch 'of 10° to 15°, This primary fold is composed 

 of a number of secondary folds of a symmetrical type, with axes 

 ranging nearly due north and south and pitching as above. Occasionally 

 the secondary folds are complicated by smaller folds or crumplings. 

 The effect of the plication structure on the rock-outcrops, and especially 

 on the topographical features, is dealt with in some detail. The latter 

 are shown to be dependent in an important degree upon the pitch, and 

 to a much smaller degree upon the dip of the rocks. 



Strike-faults play a minor role in the structure, and their effects are 

 of little importance ; they have not been observed to carry mineral 

 deposits. 



The normal faults of the district are of greater interest. They 

 range in an east-north-easterly direction, and nearly always carry 

 sulphidic ores of lead, zinc, or copper. They appear to be quite 

 independent of the folding, and behave generally as if they were of 

 later date. 



A brief account is given of the district lying on the western limb of 

 theanticlinoriumbetweenPontErwyd, Devil'sBridge, and Aberystwyth. 

 Evidence is given for assigning to the ' Aberystwyth Grits ' of earlier 

 observers a position much higher in the geological sequence than has 

 hitherto been attributed to these ' Grits '. 



The paper concludes with a tabular list of fossils, correlation tables, 

 and a description of two species of graptolites of zonal importance. 



2. " The Geology of the Neighbourhood of Seaford (Sussex)." By 

 James Vincent Elsden, B.Sc, F.G.S. 



This paper illustrates the application of zonal methods to field- 

 geology in a Chalk area. It deals with a portion of the South Downs 

 lying between Eastbourne and Newhaven. The inland outcrops of 

 the uppermost zones of the Chalk are mapped. In tracing the 

 boundary-lines fossil evidence is alone relied upon, lithological 

 characters being found untrustworthy. Certain structural features 

 of this area are thus brought to light and discussed. 



On the east of the Cuckmere River the beds examined are found 

 to be nearly horizontal. On the west side they are bent into a sharp 

 uniclinal fold, striking east and west. Seaford Head represented 

 a remnant of this fold, the westerly extension of which is destroyed 

 by marine erosion. The low ground between Seaford and Chyngton 

 occupies the trough of the fold, from which dip-slopes rise gently to 



