.part 1] of the siiales-with-'beef.' 53 



layered seams from about 1/2 inch thick, and thicker, are themselves 

 often double, each half being separated by a thin line of marl, and 

 the cones of each half do not appreciably interpenetrate. Such 

 fourfold seams readily separate at the middle, and white, crushed, 

 ■and powdery remains of small ammonites often occur between the 

 halves. The thin intervening film of marl may locally thicken 

 into a lenticle of indurated and highly calcified marl, or even into 

 •a nodule of impure limestone, in which case the beef-seam appears 

 in section to split and enwrap the nodule, which thus has an upper 

 and a lower jacket of beef (75 a, Birclii- Nodular, and see 73 g, 

 PL IV, fig. 2). In some cases (as, for example, 73 a, the lower 

 nodule-bed of Reef 20), the lower layer of beef fails to enwrap 

 the nodule, thinning out altogether on its sides. Sometimes, as 

 in 74 a (Little Ledge), the large upper and lower beef, instead 

 of enwrapping Ienticles of calcified marl, enclose layer upon layer 

 of beef with occasional filmy marl-partings. Sometimes beef more 

 than 1/4 inch thick is seen to have replaced a small ammonite- 

 shell. The ornament of the shell is then seen to appear on both 

 the upper and the lower surfaces of the beef, showing that the 

 beef takes up much more vertical room than the substance which 

 it has replaced. 



(2) Paper- shale, or laminated shale. — Brownish marl, 

 poor in calcium carbonate, splitting along the bedding-planes into 

 very thin, paper-like lamina?. The surface of each lamina is 

 generally coated with granular crystals of selenite. Paper-shales 

 appear to originate only as a product of weathering, since the 

 farther that they are followed from the surface, the less is selenite 

 present, and the less is the lamination developed. 



(3) Bedded marl. — Bluish marl, which weathers along the 

 bedding-planes ; but if it splits into thin lamina?, like paper-shale, 

 it does not, apparently, develop selenite between the lamina?, and 

 is blue rather than brown. 



(4) Conchoidal marl. — Pale bluish marl, weathering into 

 larger or smaller conchoidal masses, instead of along the bedding- 

 planes, which may, however, often be seen. It is paler than 

 the bedded marl and, presumably, more calcareous ; at any rate, 

 more so than the j)aper-shale. It suggests (passing as it does into 

 bedded marl, on the one hand, and into indurated marl, on the 

 other) a beginning of segregation of calcium carbonate towards 

 centres around which concentric lines of weakness develop, causing 

 the marl to split into polygonal blocks with curved sides. 



(5) Indurated marl. — As, for example, (71a) Reef 18 and 

 (72 a) Reef 19. An intermediate stage between conchoidal marl 

 and tabular limestone. It is paler and harder than the former, 

 softer than the latter, and weathers into conchoidal blocks. 



(6) Tabular limestone. — A further calcification of an in- 

 durated marl, passing into it above and below. The core of (53) 



