148 DREDGINGS OF THE MAEINE BIOLOGICAL ASSOCIATION: 



molluscs, etc. Colour of broken surface brown with a shade of purple, 

 and buff. Weathered surface an uniform light brown. 



A granular crystalline limestone, stained by iron in patches and 

 lines. Apparently it has always contained some free spaces which are 

 lined with larger crystal grains. Occasional almost complete rhombs 

 of dolomite of small size occur. There are slight streams of a pale 

 brown mineral of low double refraction ; and scoriaceous looking 

 inclusions of rich brown rock, containing small quartzes ; these are the 

 more aluminous parts of the rock. 



PASSAGE BEDS— TRIAS TO RHAETIC. 



M. 29a. S. 14° W. Edd., 198 miles. 



A coarse, open-textured marl or marly limestone, drab coloured. 

 The section shows widely varying colour and texture, giving at first 

 sight the effect of a detrital rock with many derived fragments. That 

 there are fragments of other marly limestones does indeed appear to 

 be the fact ; certain textures associated with definite colours, and with 

 mineral forms not found generally distributed throughout the slide, 

 are located in areas with well or less clearly defined boundaries. On 

 the other hand, the same yellow iron stain which marks some of these 

 areas runs irregularly across the section in a contorted and divided stream 

 and is always associated with a finer ground-mass than the average. 



In the general body of the rock, besides much granular crystalline 

 calcite, occur small spheroids of a clear mineral, which consist of fibres 

 radially arranged, and are also marked by a slight concentric zoning. 

 One long vein shows the same structure, and its outline is botroidal. 

 This mineral is soluble in HCl. There is a fair amount of dark 

 material, which may be carbonaceous. Not infrequent quartz grains. 

 And in the rather ill-defined orange-brown inclusions (if inclusions 

 they are) a fibrous mineral in single blades showing a double refraction 

 considerably less than that of mica ; none of this is to^be found in the 

 residue after solution in acid, and it may be gypsum. One piece of 

 certain mica is visible, with pleochroism from colourless to cinnamon- 

 brown. The residue after solution in acid consists chiefly of a rich 

 olive-brown isotropic matter in flocculent form. 



M. 29b. 



Compact, smooth, and fine-textured marl in thin slabs, can be marked 

 by thumb-nail, drab coloured. The section shows very minute grains of 

 calcite, and some brown fragments which may once have been mica. 



M. 29c. 



Angular fragment of stone-coloured marl, rather coarser than last, 

 but still fine-grained and compact, just harder than the thumb-nail. 



