158 DREDGINGS OF THE MARINE BIOLOGICAL ASSOCIATION: 



The section resembles a breccia, in which the individual grains are 

 as well fitted to each other as the fragments in a tessellated pavement ; 

 thus there is a minimum of cementing matter. But, on the other 

 hand, the normal constituents of granite, orthoclase, a little oligoclase, 

 quartz, and some brown mica occur in much the proportions that 

 would be found in a micro-granite, and very similarly distributed. 

 Some of the felspar is micro-perthite. A great many felspars are 

 cracked, some crushed, in each case the cementing material invades 

 the crystal. Many of the quartz grains are similarly cracked, and the 

 mica has been forced into curved forms to fit the surrounding grains, 

 and in some cases has been structurally destroyed. The great majority 

 of the grains of felspar and quartz show strain shadows in polarised 

 light. The cementing material consists very largely of zoisite, with 

 which is possibly a little felsitic matter. Small well-formed crystals 

 of apatite and fluid inclusions with bubbles occur in the quartz. The 

 felspar is fairly fresh and very little decomposed. 



The rock has every appearance of a fine-grained granite, crushed, 

 and then re-cemented by secondary minerals. 



But for the appearance of the worn surface this would probably 

 have passed in the hand specimen as a porphyritic felsite of tlie 

 granitic class ; it appears to agree precisely with the Mimophyrc 

 quartzeux of Brongniart, and the Granite recompos4 of French petro- 

 graphers. 



A precisely similar rock is found at — 

 M. 13a. S. 26° W. Edd., IT8 miles. 

 M. 30c. S. 21° W. Edd., 215 miles. 

 M. 44a. S. 17° W. Edd., 298 miles. Distinctly angular block. 



Its range is, therefore, about 29 miles at least. 



LIMESTONE. 



M. 80e. S. 16^° W. Edd., 48 9 miles. 



A large sub-angular stone, the surface distinctly polished. Very 

 compact and hard. Brown with a vein of lighter buff or drab, dendritic 

 markings on the lighter portion. 



The section passes through both the mass of the specimen and a 

 portion of the vein. Both consist of minutely granular crystalline 

 material, largely calcite, but apparently dolomitic. The darker part 

 gives indistinct evidence of organic remains, and shows clear rounded 

 sand grains. 



The rock is certainly puzzling, it may (doubtfully) have some 

 affinity to the Cotliam marble, but it would be a bold guess indeed to 

 so identify it. 



