378 J- F. BLAKE AND W. H. HTTDLESTON ON 



2. North- Grimston Limestone, or CoraZ i2a^ proper. — About 40 

 feet of hard limestone is wrought in the two quarries on either side 

 of the Wharram road. The stratigraphy of these beds is at first 

 sight a little difficult to understand. The Rag beds are nearly level 

 in the face of the escarpment and on the top of the plateau, whilst 

 in the quarries the beds are inclined at an angle of 20° S., or S. by 

 E. to N. by \V. (See fig. 22.) This peculiarity is more or less 

 noticeable along the whole of the southern slope of the Langton- 

 Wold ridge, of which North-Grimston Hill is an extension. If they 

 really are the same beds as those seen on the escarpment, their 

 strong dip is due probably to the undermining action of water upon 

 the softer beds below, whereby the harder beds are bent down, and 

 in some cases almost snapped off from their horizontal continuations. 

 The Hag of the escarpment, however, shows little or no flint, 

 whereas the lower portions of the hard Rag of the quarries is full 

 of it. How to account for the difference is one of the difficulties 

 of this most puzzling section. The alternative possibility is that the 

 whole group is a series of false-bedded accumulations. 



In the quarries the hard Rag (2 of section, fig. 22) presents two 

 phases. Without detailing the beds, the following is a description, 

 taken principally from the upper quarry, in descending order : — 



a. Buff-coloured limestones with yellowish markings ; beds of ft. in. 



white stone, seldom hard and crystalline like the series 

 below. Indications of corals moderate : flints rare. Spines 

 of Cidaris florigemma less plentiful. C. Smithii and Hemici- 

 daris intermedia numerous. Beds less shelly than lower 

 series, but contain a fair assemblage of some of the Rag- 

 fossils, Nerinaa, Littorina pulchcrrima, Opis, &c, along with 



Pentacrinites and Apiocrinus about 20 



N.B. At Grimston Field, where the junction of this 

 series with the cement-stone (1 of sect.) may be noted, a 

 specimen of Nautilus aganiticus, Schlot., not hitherto found 

 in the Corallian of England, was secured. 



b. Soft yellowish brash, with Ammonites varicostatus 4 



c. White sparry and compact limestones in strong blocks, 



which become largely charged with flint, especially about 

 6 ft. above the base of the series. Beds full of fossils : 

 fauna megalom orphic * 17 



d. Urchin series (3 of section, fig. 22) 



37 4 



Some of the beds are very rich in shells ; but these are frequently 

 so glued into the general mass of the limestone as to be difficult of 



* This division (c) is the chief fossil-bearing series of North Grimston. 

 The lower portions are very siliceous ; and there are great masses of flint 

 both parallel with the bedding and lining the diagonal fissures, as well as 

 masses which seem developed in the interior of the blocks. Some of the 

 masses of flinty chalcedony seem to throw light upon the origin of flint and 

 chert in limestone. There is an abundance of a small Ostrea (Exogyra nana ?), 

 the shells of which are more or less "beekised;" whilst in some of the beds 

 the silicification appears in connexion with Thecosmilia. The original structure 

 of the limestone is very well preserved in specimens of these flints : one which 

 includes a section of Pyg aster shows this very well, the peculiar markings of the 

 limestone, so different from those of ordinary oolite, being faithfully transferred 

 to the replacing substance. We have already seen how faithfully true oolitic 

 structure is copied in the flints fvom the Lower Limestones of the Pickering 

 district. 



