1912.] 



NOTES ON GEOLOGICAL RESULTS. 



375 



REPORT ON ROCKS. 



1. — Cherbourg. — " This rock has a schistose aspect 

 " and has been obviously much affected by pressure, being 

 "very fissile. In colour it is a pale greenish-grey, resembling 

 "a phyllite more than a normal crystalline schist. Under 

 " the microscope a slice gives indications of stratification 

 " (more or less disturbed) by a slight banding of the material. 

 " It shows much mineral change, on a small scale, consisting 

 " of a pale green flaky mineral, the exact nature of which — 

 "whether a hydrous biotite or a chlorite (neither very rich in 

 "iron) is difficult to determine, but one ov two larger flakes, 

 "here and there present, induce me to think it the former. 

 "There are numerous very minute needles (? rutile) and a 

 "clear mineral, which probably represents a felspar ; much of 

 "it, at any rate, very likely secondary. The rock has a 

 " general resemblance to phyllitic slates of early Cambrian or 

 "late Pre-Cambrian age." 



This rock is therefore microscopically what it is known 

 to be in the field. 



No. 2. — From Glaciated Clay, Guernsey.— " This 

 "is more distinctly green in colour than No. 1, looks more 

 "powdery, but is distinctly fissile (cleavage). Under the 

 "microscope the slice shows distinctly a cleavage foliation, 

 "with signs of great crushing. The constituent minerals are 

 "partly the above-named green mica, or chlorite (minute), 

 " partly a felspathic constituent in association with it, some- 

 " times earthy looking (probably from crushing and decom- 

 " position). Hei e and there is a rather long phacoidal lenticle, 

 " composed of the same minerals, but the felspathic is more 

 "fragmental in aspect and rather larger. Occasional spots 

 " and lines of a brown staining, and not a few microliths, both 

 " clear and opaque, but too irregular in shape or small in size 

 "for identification. It is difficult to be sure, but I incline to 

 "regard it as a highly crushed and altered diabase rather than 

 "a pressure modified sediment. Microscopic examination 

 "does not suggest a close affinity to the Cherbourg rock, 

 " to which, in the hand specimen, it has a fair resemblance." 



It is therefore consistent with the whole facts to say that 

 the clay specimen is locally derived. 



No. 3. — Fissile Green Schist from Les Tielles. 

 — " This is certain, that the rock has been greatly crushed, 

 " owing to that, its structure and, perhaps, its mineral character. 

 " The microscope shows a great deal of rather wavy pale- 

 " green micaceous mineral, probably a hydrous biotite rather 



