302 MARKER : NOTES ON NORTH OF ENGLAND ROCKS. 



pellet of calcareous brown mud. Some show a feature often 

 observable in such rocks ; viz., they are composite, enclosing two or 

 three pellets or organic fragments in one shell or mantle. The 

 matrix of crystalline calcite contains some angular quartz-granules 

 without any coating. 



This frame-work of calcite, occupying one-third or one-fourth of 

 the bulk of the rock, must be regarded as of posterior origin to the 

 accumulation of the deposit, and is by no means essential. The 

 oolites of other districts often lack this matrix, and have in conse- 

 quence a porous texture. Such is the case in some of the building- 

 stones derived from the Lincolnshire Limestone, which is a thicker 

 development of the Millepore Oolite. The specimen sliced [1090], 

 from the Ancaster quarries, shows the grains to be loosely compacted 

 without any cementing material. The organisms seen are for the 

 most part foraminifera and chips of brachiopod shells showing 

 a laminated or fibrous structure. Many of the grains consist of 

 a pellet of amorphous material surrounded by the usual coating, in 

 which a radial as well as a concentric structure is well marked. 



We pass on to the next calcareous member of the Yorkshire 

 Oolites, the Scarborough Limestone. Our specimen [946] is a rather 

 gritty grey limestone from the beach below AVheatcroft, Scarborough. 

 It contains abundance of little irregularly shaped grains of quartz, 

 which have sometimes fluid-pores, sometimes glass-cavities, and are 

 probably from more than one source. The chief fossil remains are 

 scraps of shell probably belonging to Pedeti. These and the quartz- 

 grains are embedded in a crowd of minute yellow crystals, which are 

 either chalybite (the carbonate of iron) or perhaps a ferriferous 

 dolomite. Each little crystal has an opaque centre, probably of 

 pyrites. 



One of the nodular iron-stone bands at the^same locality was also 

 sliced [947]. This too has little scattered angular grains of quartz 

 enclosing fluid-pores ; but the great bulk of the specimen consists of 

 minute yellow crystals of chalybite. The quartz-grains are often 

 fractured, and the cracks filled in with the jyellow ground-mass of 

 chalybite. The slide shows here and there a red-brown stain of 

 iron-oxide. 



Our specimen of the Cornbrash from Gristhorpe Bay [1022] again 

 shows numerous angular grains of quartz. It contains a great 

 variety of organic fragments. Some scraps of lamelli branch shells, 

 originally no doubt composed of aragonite, have been converted into 

 patches of crystalline calcite-mosaic, while calcite shells, either 

 brachiopods or some oyster-like bivalve, retain their proper structure. 

 Little oval sections, each behaving as a single crystal of calcite, must 



Naturalist, 



