124 DREDGINGS OF THE MARINE BIOLOGICAL ASSOCIATION: 



fairly numerous fluid inclusions of very small size. No other mineral 

 is present. The rock must be classed as an aplite. 



Similar rocks to 24g are 34e, S. 28° W. Edd., 18-5 miles and 14e, S. 24° W. 

 Edd., 20 miles. 



FELSITES. 



Under this heading are placed a number of rocks which fall readily 

 into three groups, the first of which consists of two specimens, almost 

 identical in character, and very familiar in appearance to any one who 

 has an acquaintance with the Permian and Triassic rocks of Devon. 



M. 27c. S. 19° W. Edd., 18-3 miles. 



Compact red-purple felsite, with light porphyritic felspars and black 

 mica. Fracture trachytic. Has all the appearance of one of the new 

 red felsites. 



M. 41a. S. 36J° W. Edd., 26-6 miles. 



Felsite, texture trachytic, colour red-brown, small dull white por- 

 phyritic felspars, and a little black mica. Cryptocrystalline ground- 

 mass. A few idiomorphic felspars. A few porphyritic quartz crystals 

 with corroded outlines. Well developed, highly pleochroic brown mica. 

 The ground-mass contains numerous microlites, also many small fel- 

 spars outlined in or largely replaced by hematite. Flakes of hematite 

 are very numerous. A typical red-rock felsite. 



The specimens placed in the second group form a series, commencing 

 at the Hand Deeps and terminating M. 62, 46-4 miles S. 25° W. from 

 the Eddystone. Of these the northernmost example has been subject to 

 considerable mineral alteration ; the southernmost is the most fresh, 

 and in the latter the porphyritic constituents are more prominent than 

 in any other. The northernmost is probably alone in that it contains 

 mica. All are strongly reminiscent of rocks elsewhere associated with 

 the Permian and Trias. 



354/3d. Slopes of Hand Deeps. 



A grey rock, with a slight shade of green and small purple spots. 

 Small felspars appear, colour buff, all somewhat decomposed. At 

 places the tint of this rock varies to yellow and to purple. There are 

 minute black specks of a hard mineral, and calcite is developed on 

 joint faces. 



Microscopically the ground-mass is seen to be crypto-crystalline 

 with much minute calcite, areas of which mineral also occur. Small 

 felspars are scattered through this mass, and are about uniformly 

 divided between orthoclase and plagioclase. Quartz occurs in small 

 patches of interlocked granules. Mica is now almost entirely replaced 

 by pseudomorphs in limonite and magnetite. 



