Yol. 59.] SOUTH DEVON AND THE MIDLANDS. 319 



The Gres de May is now only represented by a few small isolated 

 patches ; but it is evident that it was once a large and thick 

 formation. Small as the exposures are, however, they are of con- 

 siderable commercial importance. At May, where the rock is 

 quarried for paving-stones, it has a thickness of 985 feet, but the 

 outcrop is less than 3 miles in length, with a width of half-a-mile. 

 The beds dip at an angle of about 45°, and consist mainly of a tough 

 massive quartzite of medium grain and with conchoidal fracture. 

 This alternates, however, with dark fissile seams and with sand- 

 stones which are generally pink. The characteristic hard quartzite 

 is of various colours : it may be nearly white to various shades of 

 red, and sometimes it is grey or brown. The red coloration occurs 

 very irregularly, and is due to infiltration. Prof. Bonney has 

 detected a deposit of ferrite. This infiltration can frequently be 

 seen to have penetrated along joints and bedding-planes, and near 

 the base of the Gres de May there is a ferruginous band. In the 

 Gres Armoricain there is a deposit of red haematite, which is still 

 worked in the vicinity of May and at other places ; and I observed, 

 in passing through the village of Eeuguerolles during a shower of 

 rain, that the flood-water was stained red. 



The Gres de May at this place is on the banks of the River Orne, 

 and has been exposed by valley-erosion, as is the case at Gouvix, 

 in the valley of the Laize. At both these places human agency is 

 rapidly accelerating the work of Nature. 



In other localities the Gres de May, although of small superficial 

 extent, constitutes the dominant ground of the district. It forms the 

 summit of a ridge near the village of Jurques, at an altitude of 

 1185 feet. It is here a white quartzite, fossiliferous, and usually 

 free from the red staining. It occurs again at Montpincent, the 

 highest point in the Calvados, where it is also of a whitish colour. 

 There are only shallow workings in it for the purpose of road-making, 

 but its comparative hardness doubtless accounts for its elevated 

 position. 



There are other detached exposures of the Gres de May near 

 Falaise, and at various other localities in the Calvados. It is evident 

 that we have in these the last surviving remnants of a formerly 

 extensive and important deposit, which was originally the bed of the 

 Ordovician sea. And, when we have regard to the extent and the 

 original thickness of the deposit, we can see that it was capable of 

 furnishing abundance of material, not only for the Ordovician 

 pebbles of the Budleigh-Salterton Pebble-Bed, but also for a great 

 deal more. Davidson 1 pointed out that there were many Lower 

 Devonian fossils in this pebble-bed. This fact renders it extremely 

 probable that the Devonian was once represented in those parts of 

 Xormandy where now only the Ordovician is found. 



The denudation has been less severe in the case of the lower 

 members of the Ordovician Series, which still occupy a considerable 

 area. As a whole, the Gres Armoricain, with its associated rocks, 



1 < Monogr. Brit. Foss. Bracb.' vol. iv (1881) p. 323 (Palaxmt. Soc. vol. xxxv). 



