2^8 DE. C. A. MATLEY ON THE [JuHG I912, 



probably also part of the same deposit as the Arden Sandstone. 

 The mapping of this Leicester sandstone was revised about 1900 

 b}' C. Fox-Strangways, who stated ^ that it 



' appears to occur in more or less lenticular ru asses, which thin out in all 

 directions, and there is no evidence that this bed is so continuous and regular 

 in its character as it has been supposed to be.' {0]). cit. p. 11.) 



He also figured an instructive section showing the sandstone passing 

 laterally into grey marly beds. In his map, however, partly for 

 economic reasons, he differentiates only the 'principal mass of coarse 

 sandstone ' from the Keuper Marls; whereas, in the earlier edition, 

 the sandstone was mapped as a group or zone including the asso- 

 ciated grey marls, shales, and 'skerries.' Regarded as a group, 

 the horizon is probably as persistent as that of Warwickshire, and 

 Fox-Strangways admitted that these beds ' occupy a fairly definite 

 horizon ' (op. cit. p. 13). 



The Arden Sandstone Group seems, therefore, to be part of a 

 deposit which was laid down over an area extending at least 

 70 miles from north-east to south-west ; it probably also thinned 

 out south-eastwards. It was formed at a time when ' continental ' 

 conditions in Britain were nearly at their close, and it appears to 

 me that the most satisfactory explanation of this sandstone zone is 

 that it was probably formed, as an episode in the deposition of the 

 Marls, when the open sea gained a temporary access to the Keuper- 

 Marl area and brought with it the fishes and molluscs whose 

 remains are now found in the zone. It represents, in fact, a 

 phase corresponding to that of the Ehsetic Bone-Bed and the Tea- 

 Green Marls, but of somewhat earlier date. 



The associated Keuper Marls have been dealt with, mainly in 

 regard to their stratigraphical relations with the Arden Sandstone, 

 and no special attention has been devoted to the vexed question of 

 their origin. But my observations, so far as they go, tend to confirm 

 the view of the older observers that the Marls are aqueous deposits, 

 though possibly consisting largely of wind-borne material, deposited 

 in a comparatively, and sometimes quite, shallow lake undergoing 

 strong evaporation and subjected to occasional irruptions of the sea. 

 They represent the closing phase of Triassic ' continental ' con- 

 ditions in the English Midlands, when the slow sabsidence which 

 was soon to bring in marine Rhsetic and Liassic deposits was in 

 progress, and produced that overlapping of the Keu|]><er rocks on to 

 the higher grounds of the Triassic land-surface which is observable 

 in the neighbouring districts of the Lickey Hills, K'uneaton, and 

 Charnwood Forest. 



YIII. Tectonics of the Aeea. 



One of the most interesting results of the mapping of the Arden 

 Sandstone Group is the light that its stratigraphy throws on the^ 

 geological structure of the area, which is now seen to be by no 



^ 'The Geology of the Country near Leicester' (Espl. of Sheet 156) Mem. 

 Geol. Surv. 1903, pp. 11-13. 



