Thomson. — GcoUjc/ji of Middle Clarence and lire Valleys. 315 



flint-beds do not seem to persist to the west into the Swale, but about 

 a mile and a half above the junction with the Ouse there is a series of 

 banded sandstones and mudstones, striking east-north-east, and dipping 40° 

 to the north-north-west, which probably represents the lower sandstones. 



The Sawpit Gully mudstones are clearly exposed in the steep bed of 

 Sawpit Gullv (Plate XXVI, fig. 1), and consist predominantly of black 

 mudstones, but occasional thin beds of sandstone are found. There is 

 some folding in the section, but, on the whole, the dip is to the north- 

 north-west, like that of the overlying flints and limestones. Calcareous 

 concretions up to 1ft. in diameter are common in the upper 400 ft., but 

 below that they are rarer. In the uppermost 15 ft. pyritous nodules are 

 abundant, but they do not persist far downwards. At the actual junction 

 with the flint-beds there is a strong yellow efiiorescenc^^ The junction 

 appears to be quite conformable. Inoceramus concentric is var. jjorrectus 

 was obtained 20 ft. below the junction and also at about 100 ft. The 

 ammonite Gaudryceras saijci was obtained in a large concretion about 

 300 ft. below the junction. 



The Sawpit Gully beds are exposed in the Nidd above the flint gorge, 

 where the valley again opens out in the softer rocks. Near the base 

 there is a band of sandstones and sandy mudstones containing a large 

 species of Inoceramus. The higher beds are fine-grained black mudstones 

 with small concretions, in which fragments of crustaceans were observed. 



In the Swale, owing to slips and talus slopes, there is not a continuous 

 exposure of the Sawpit Gully beds. Not far from the top there is some 

 sharp folding of the beds, causing local reversals in the direction of the 

 dip (Plate XXVI, fig. 2). From the highest exposure concretions containing 

 numerous specimens of AucelUna euglypha and fossil wood and plant- 

 impressions were obtained. 



The thicknesses given above for the various divisions of the Clarentian 

 at Coverham were estimated, except in the case of the conglomerates, 

 by measurements from a section drawn to true scale. An average dip 

 of 55° was allowed, but it wiU be observed that the dip is often steeper 

 and seldom less than that figure. The reversals of dip due to folding are 

 unimportant, but have been allowed for. An almost continuous section 

 of the beds has been observed, and no faults of any consequence were seen. 

 Consequently, unless there is a very strong unconformity between the 

 Clarentian and the Amuri limestone and a repetition of the beds by closely 

 appressed folds, there is no escape from the conclusion that the thickness 

 given is approximately correct. Hector and McKay agree in estimating 

 the total thickness up to the " grey marls " as approximately 12,000 ft. 

 Woods remarks that the thickness, if correctly estimated, is very great 

 in view of the unity of the molluscan fauna. 



The beds are marine throughout, and calcareous concretions are abund- 

 ant, but plant-remains and fossil wood are found in the sandstones and 

 concretions from top to bottom. The black colour also of the mudstones 

 and sandy mudstones is doubtless due to the presence of carbonaceous 

 matter. Glauconite has been observed only in the greenish sandstones 

 of the Nidd beds. The above facts, together with the rapid lateral 

 variation in the sandstones and the presence of the pebbly mudstones 

 in the lov/er beds, suggest that the whole series was deposited as the 

 topset beds of a continental shelf undergoing rapid depression and near 

 the mouth of a large river, the sands and gravels of which were arrested 

 nearer shore or up the estuary by its drowning. 



