318 MR. 0. A. SHRIJBSOLE ON TEIASSIC PEBBLES OF [Aug. I903, 



the supposed ' mid-Channel ' source falls into this category, if we 

 admit that the English Channel had then no existence. 



Some part or extension of Cornwall has also been mentioned as a 

 possible source. A few Ordovician fossils of southern type have 

 certainly been found here, but, I believe, no purple quartzites. 

 And Cornwall is not exactly the direction in which we should 

 naturally look, for it does not seem to supply the necessary physical 

 conditions ; although, as Prof. Bonney has shown, it was part of the 

 ancient Armorican massif. 1 But it was proved by Davidson 

 that the fossil-evidence is insufficient, for only two Gres-de-May 

 species of Budleigh Salterton are found at Gorran Haven, while the 

 Gres Armoricain is unrepresented. 2 



We have to look, then, for a region — 



(a) In the direction of the thickening of the Pebble-Bed ; 



(b) of sufficient extent and height to have furnished the mass 



of the pebbles ; 



(c) which contained in Triassic times the same hard rocks 



as those that are found in the Pebble-Bed, and no others. 



III. The Gees be Mat of Nokmandy, and its Associateb Rocks. 



In the Armorican peninsula we have an example of an old land- 

 surface which has been so worn by long exposure to denuding 

 agencies, that over the greater part of Britanny nothing but the 

 granitic core with gneisses, etc. is left. The original height of the 

 massif can only be guessed at ; but Prof. Bonney remarks that its 

 breadth, including the connected area, must have exceeded that of 

 the Alps. 3 In parts of Normandy, however, this process of wasting 

 was arrested by the deposition of Mesozoic sediments ; and these 

 again have been denuded, so that the old Palaeozoic rocks are usually 

 but thinly covered, or are once more exposed at the surface, while 

 the rivers have everywhere cut into the older rocks. Even in 

 Normandy a large part of the surface is occupied by the Phyllades 

 de St. L6, which are considered to be of Archsean age, and form the 

 characteristic soil of the Bocage. 



The Paleozoic rocks are represented in descending order princi- 

 pally by the 



Gres de May. 



Schistes Ardoisiers (Schistes d'Angers). 



Gres Armoricain. 



Purple ' Schists ' ] ^ , . t,., , ., 



xy r i n 1 , y =Gres a Bilobites. 



Purple Conglomerate J 



The Gres de May is further subdivided as under : — 



A. Gres du sommet (Conularia pyramidula, Homalonotus Deslongchampsi, 



Modiolopsis Morierei, M. prima). 



B. Niveau schisteux a Trinucleus Bureani, with Calymene Tristani, etc. 



C. Gres a Homalonotus {Homalonotus Vicaryi, H. serratus, H. Brongniarti, 



with Plcesiacomia brevieaudata, Dalmanites incerta). 



D. Gres minces de la base, a Calymene Tristani. Often ferruginous. 



1 Quart. Journ. Geol. Soc. vol. xliii (1887) p. 320. 



2 ' Monogr. Brit. Foss. Brach.' vol. iv (1881) p. 330 (Palseont. Soc. vol. xxxv). 



3 Quart. Journ. Geol. Soc. vol. xliii (1887) p. 320. 



