132 Physiography of N. Britain in Millstone Grit Times. 



shire in early Grit times are afforded in several areas. Pre- 

 liminary oscillations produced rolled shell beds (' beach 

 beds ') at the top of D-, near Castleton, in Derbyshire (Barnes 

 and Holroyd, Trans. Mchr. Geol. Soc, Vol. XXV., p. 119), 

 Winterburn Reservoir, Yorkshire (Tiddeman, Proc. Yorks. 

 Geol. Soc, Vol. XL, (1891), p. 490), Pythorn and Brock- 

 thorns, both near Slaidburn, and near Grassington, Yorkshire 

 (Hind, Proc. Yorks. Geol. Soc, Vol. XIV., pp. 428, 431, 

 432), and Newton Gill, Long Preston, Yorkshire (Hind and 

 Howe, Q.J.G.S., Vol. LVIL, p. 360). It was a very uneven 

 floor on which the Grit rocks were laid down (' Yorkshire 

 Coalfield,' map facing p. 32). Around Great Whernside it 

 very much looks as if a considerable thickness of the chcrty 

 beds of Swaledale had been cut out either by non-deposition or 

 subsequent erosion, as the Basement Grit rests on beds well 

 down in the Yoredale sequence (see Dakyns, Proc Yorks. 

 Geol. Soc, Vol. XL, p. 358). The Pendleside Series thins 

 out to nothing at about the latitude of Settle (see Hind and 

 Hawe, Q.J.G.S., Vol. LVIL, p. 363), and by analogy it seems 

 quite probable that the Grits themselves rapidly thinned out 

 north of the Swale. It is not certain that the outliers on the 

 mountain tops of the Wensleydale-Swaledale watershed are 

 of early Grit Age. On the contrary they may be comparatively 

 late. 



The Pendleside Series is overlapped by the Grits, and the 

 Grits are overlapped by the Coal Measures, all of which 

 points to a relatively small area of deposit at first, gradually 

 enlarged by subsequent depression. The absence of fresh- 

 water shells in the Grits, and their abundance in the Coal 

 Measures, suggests to the writer that the Grits are in the main 

 estuarine, and the Coal Measures deltaic. 



If the above suggestion be correct, it seems likely that the 

 current bedding may be, in many cases, at right angles to 

 the general axis of the estuary, and this may require to be 

 borne in mind in considering this section of the evidence. 



The field evidence of the Lower Grits shews that they thin 



in an eastern direction and become finer in grain, for example : 



(a) The Lancashire Grits (Pendle area) are much 



thicker than the Yorkshire Grits. (In this 



connection see Hull, ' On Isodiametric Lines,' 



Q.J.G.S., Vol. XVIIL, p. 127.) 



(1^) The Basement Grit of Great Whernside, when traced 



eastward down Coverdale, rapidly becomes a 



mass of shales and thin sandstones (Dakyns, 



Proc. Yorks. Geol. Soc, Vol. XL, p. 361). 



(c) The thick grits of the Bolton Abbey area {K-\-P= 



2000 ft. vide Survey i in. Geol. Map. 92 N.E.) 



thin to 1400 ft. of mixed grits and shales in the 



Naturalist 



