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WALTER KEEPING ON THE 



Fossil localities, other than those already given, are : — 

 Parson's Bridge, and Temple Mine, south of Pont Erwyd. 



Monograptus lobiferus, M l Coy. 

 Climacograpsus scalaris, His. 

 Nereites Sedgwickii, Murck. 



Myrianites M'Leayi, Murch. 

 Buthotrephis major, Keep. 



Cefn Coch, near Aberystwyth. 



Monograptus Sedgewickii, Parti. 

 Buthotrephis major, Keep. 

 minor, Keep. 



Eetiofucus extensus, Keep. 

 Palseochorda tardifurcata, Keep. 



Constitution Hill, Aberystwyth ; Wern Grug, Llanilar ; Mynydd 

 Bach : Plas Crag, Llanbardarn, and other places have also yielded a 

 few fossils, mostly Algae, — Buthotrephis major, B. minor, B. minimus, 

 Keep., Palceochorda tardifurcata, Metiofucus extensus, and Nema- 

 tolites Edwardsii, Keep. 



Thickness. — We have seen that much of the apparent thickness of 

 the Aberystwyth grits is deceptive, being explained away by great 

 folds. Still a great series remains, well attested even by the simple 

 heights of many hills which are built up entirely of this group. 

 Mynydd Bach appears to be over 1000 feet high (by aneroid) ; and 

 I should estimate the group at certainly not less than 1000 feet of 

 maximum thickness. Our detailed measurements along the Devil's- 

 Bridge road show a thickness of 1639 yards, or nearly one mile. 



The Metalliferous-slate Group. — A very large part of Cardi- 

 ganshire is constructed of this series. In the special area of our 

 work it forms a broad semicircular zone, some eight to ten miles 

 across, sweeping around the dome of the Aberystwyth grits to form 

 all the slaty country from north of Cardigan up to Machynlleth. 

 At the latter place it forks into two, the main curve being continued 

 out to sea by the Dovey valley, while a broad but rapidly attenu- 

 ating arm runs northward to Dinas Mowddwy, at which place its 

 much diminished representative is found between the Bala series 

 and the Tarannon shale. 



The above area, however, is not unmixed metalliferous slate, the 

 upper part of the Aberystwyth group being brought up by folds, 

 along north-and-south lines, running through Ystrad Meurig, and 

 the Devil's Bridge ; and possibly some outliers of the Plynlimmon 

 group may be folded in. Still the general absence of arenaceous 

 beds is marked over miles of country without a single grit-bed to 

 serve for road- or building-stone. Tin Llidiart village uses the hard 

 pale slate of Goginan for building ; and at Llanafon the numerous 

 boulders serve for road-metal. 



Further south, in the line between Cardigan and Llandovery, the 

 slate series appears in still greater extent, which is due to its there 

 representing also the . Aberystwyth group, and perhaps also the 

 Plynlimmon grits, these groups not being developed as such in that 

 area. 



A marked lithological character distinguishes this group as a 

 whole, the terms "indurated shaly slate," "irregular slate," "flaggy- 

 slate," " pale blue slate," from my note-book, serving to indicate the 

 usual character; I also find "hard pale slate-rock, often much 



