YOKED ALE ROCKS. 1 65 



correspond to the same point of time, while the formation of lime- 

 stone may have gone on longer at some spots than at others.^ 



The Yoredale rocks present no very special palceontological 

 features as distinguished from the Carboniferous Limestone ; they 

 comprise beds of marine, and, possibly, estuarine origin, and some 

 that are suggestive of fluviatile and terrestrial conditions. 



The fossils are for the most part marine, but fewer in number 

 than in the Carboniferous Limestone. 



Among the fossils of the Yoredale series, occurring chiefly in 

 the limestones, are Oiihoceras Steinhaiierii, Nautilus cyclostomiis, 

 Goniatites sphceriais, G. Listeri, and other species, Posidonomya 

 Gihsoni, Aviculopccten papyraccus, Spirifera glaber, Productus semi- 

 reticiilatus, Phillipsia gemmuUfera, etc. Fossil plants, such as Siig- 

 man'a, Calamites, etc., are likewise met with. 



Fish-remains, belonging to the genera Petalodiis, Lophodiis, Psani- 

 modiis, and Pleufodus, have been found in some of the upper lime- 

 stones of Yoredale.^ Mr. Home, of Leyburn, has discovered relics 

 of a large Labyrinthodont in the upper part of the Yoredale rocks, 

 above the main Limestone, in a railway-cutting near Leyburn, in 

 Yoredale (Wensleydale).^ 



The Yoredale Rocks extend from the coast of Northumberland 

 round the western borders of Durham to Ingleborough, forming 

 the principal part of the moorlands that lie to the east of the 

 Pennine fault.* (Seep. 151.) 



Near Halifax the Yoredale strata (including the shales of Hebden 

 Bridge) attain a thickness of 600 feet. They form a somewhat 

 different type of the series, formerly known as the Upper Lime- 

 stone Shales, and extend south of the Craven fault as far as 

 Derbyshire. Over a great part of North Y'orkshire all sandstones, 

 coarse and fine, are known as grits.* 



At Harrogate beds formerly classed with the Millstone Grit were subsequently- 

 placed in the Yoredale series by Prof. PhilHps ; these include the Spofforth Haggs 

 roadstone (10 feet), the FolHfoot coal-grit (30 feet), the Almes Cliff grit (50 feet), 

 the Harrogate Tunnel sandstones (20 feet), and the Harrogate roadstone (50 feet) ; 

 interstratified with these beds are shales, sometimes containing Stigtnaria. The 

 beds are grouped as follows : — 



Upper Shale. 



Calciferous Encrinital Grit (Harrogate roadstone). 



Lower Shale. 



Lower Grits. 



In Edenside, finely-laminated siliceous beds are associated with 

 the limestones of the Yoredale rocks, and they occasionally pass 

 into beds of nearly pure chert, notwithstanding their obviously 



^ Geology of the Yorkshire Coal-field, pp. 12, 13. 



"^ J. W. Davis, Q. J. xl. 614. See also West Yorkshire, by J. W. Davis and 

 F. A. Lees, edit. 2, p. 99. 

 ■ 3 L. C. Miall, Q. J. xxx. 775. 



* Sedgwick, T. G S. (2), iv. plate 5, fig. 3. 



" On the formation of grit, see Dr. H. C. Sorby, Proc. Geol. and Polyt. Soc. 

 W. Riding, iii. 232, 372, 669. 



