THE GEOLOGY OF THE ENGLISH CHANNEL. 185 



Two Diabase. Nos. 17, 37. 



H. 17. Trawled 17 to 18 miles S.W. by W. of Start Point. Weight 7 to 

 8 cwt. 



A dark green rock of medium grain, with minute specks of pyrites. A 

 diabase of ordinary type. The plagioclase is much decomposed, the twinning 

 being often lost. Quartz has been secondarily deposited. The augite has also 

 been partly attacked by decomposition, and chloritic matter has resulted 

 thereby. A little apatite is present. Magnetite or black oxide is much more 

 abundant than the pyrites. — E. B. T. 



H. 37. Trawled 15 miles S.S.W. of Start Point. Weight 7 to 8 cwt. 



A rather compact, dull, greenish-grey crystalline rock. Microscopic 

 examination shows it has once been a fine-grained but holocrystalline rock, 

 composed mainly of plagioclase felspar, augite, and some iron peroxide ; but it 

 is now composed of more or less altered felspars, associated with viridite and 

 chloritic minerals, epidote and other secondary products, and perhaps some 

 altered augite.— T. G. B. 



Three Gabbro. Nos. 8, 15, 38. 



H. 8. Trawled about 25 miles S.W. of Start Point. Weight 5 to 6 cwt. 



A coarse-grained rock consisting of white opaque felspar crystals and 

 yellowish-grey diallage. Microscopic examination shows no other constituents ; 

 the felspar is almost entirely decomposed, scarcely showing original optical 

 features. The diallage at borders sometimes undergoes a change into 

 actinolite. — E. B. T. 



H. 15. Trawled about 16 miles S. of Start Point. Measures 2' 8" x 1' 8" 

 X 1'6". 



To this block some ' killas ' was adherent, so that it was a junction speci- 

 men. The diallage scarcely retains its own physical properties ; much of it 

 has become altered to an aggregate of diverging fibrous, colourless or pale 

 greenish crystals, which may probably belong to the actinolite group. The 

 plagioclase is in places opaque from decomposition, and is everywhere much 

 penetrated by the pale green actinolite microlites. — E. B. T. 



H. 38. Trawled 15 miles S.S.W. of Start. Weight 10 cwt. 



A moderately coarse-grained compound of a bluish-white felspar and a dull 

 green mineral. Microscopic examination shows that it is a considerably 

 altered gabbro. The plagioclastic felspar is to a very large extent replaced by 

 micromineral products, such as occur in the so-called saussurite. The augite 

 or diallage is replaced by hornblende, sometimes normal in aspect, sometimes 

 rather actinolitic. An iron oxide and a little apatite are present, but no 

 indication of former olivine. — T. G. B. 



One Serpentine. No. 6. 



H. 6. Trawled 13 miles S.S.W. of Start Point. Weight 5 cwt. 



Mottled red and green colour, with steatite veins, and precisely like some ol 

 the Cornish varieties. 



