Geological Society of London. 331 



by the elevation of Holland after the deposition of the Amstelien 

 and a subsidence in Suffolk, which carried the Chillesford Beds over 

 an area which was not covered by the Norwich Crag sea. 



No equivalents of the Weybourn Crag or of the Cromer beds 

 (Forest Bed series) have been found in the Dutch borings. These 

 are to be referred to the Pliocene, as pointed out by Mr. Reid, but 

 possibly some of the unfossiliferous pebbly gravel of Norfolk and 

 Suffolk may be Pleistocene. 



The Weybourn Crag marks a re-invasion of East Anglia by the 

 sea ; but previously to the deposition of the Cromer beds the southern 

 margin of the Pliocene gulf had again retreated to the north, and an 

 estuary, similar to that of the Chillesford Clay but situated farther 

 east, received the waters of the Rhine, which brought down the 

 drifted remains of mammalia and some southern mollusca. 



The newest portion of the Cromer deposits is of an Arctic character, 

 and seems to show that no great interval separated the Pliocene and 

 the Pleistocene periods. 



A second subsidence of the Dutch area took place in Pleistocene 

 times ; the Glacial and post-Glacial beds being 600 feet thick under 

 Amsterdam. No Till or contorted Drift similar to the deposits occur- 

 ring in East Anglia and in the district north-east of the Zuyder Zee 

 has been met with in these borings. The glaciation of Holland pro- 

 ceeded from the Baltic, and not from Norway, and the Baltic ice does 

 not seem to have reached the Dutch coast ; still less could it have 

 travelled thence in the direction of East Anglia. 



The two prominent physical features of the Pliocene period were 

 the Rhine and the basin of the North Sea. The hypothesis of a 

 permanent basin with shifting shore-lines, in contiguity to which 

 the shallow-water deposits of the Upper Crag were deposited, seems 

 to agree with all the facts of the case, and to throw light on the 

 geographical conditions of the Pliocene epoch. 



2. " The Lingtda-Flags and Igneous Rocks of the Neighbourhood 

 of Dolgelly." By Philip Lake, Esq., M.A., F.G.S., and S. H. 

 Reynolds, Esq., M.A., F.G.S. 



The area dealt with in this paper lies south and west of Dolgelly, 

 between the Arthog road and the hill called Mynydd Gader, which 

 lies in front of the precipices of Cader Idris. The stratified rocks 

 belong to the Middle and Upper Linyula-Fl&gs and Tremadoc Slates. 

 The Middle Linyula-Flags (Ffestiniog Series) consist of bluish slates 

 with grit-bands containing the usual Lingulella, passing into Upper 

 Lingula-Flags (Dolgelly Series) consisting of dark slates with Orthis 

 lenticular is, Parabolina spinulosa, etc., and containing two andesitic 

 lavas. These pass into the basal Tremadoc Slates, with Dictyoyraptus 

 flabelliformis, surmounted by an upper volcanic series with rhyolitic 

 lava. Subsequent intrusions of diabase occurred, of a laccolitic 

 character, but of such a nature as to lead the authors to suggest the 

 possible intrusion of the diabase along a line of unconformity in one 

 case ; there is, however, no newer rock above the diabase to indicate 

 of what date the overlying beds would be if such unconformity 

 occurred. It is further shown that the important faults in the area 



