190 Correspondence—Miss O. A. Raisin. 
THE METAMORPHIC. ROCKS OF SOUTH DEVON. 
Srr,—The writer of the letter printed in your January issue 
on this question (p. 46) does not seem quite to recognize the 
position which the microscope occupies in the investigation. As 
Professor Bonney in his previous letter to your journal kindly 
alluded to my work in the district under discussion, I may perhaps 
be allowed briefly to indicate the point, which, as it seems to me, is 
rather overlooked by Mr. Somervail. How he can have supposed 
Professor Bonney has anywhere stated that the microscope in 
geology is “everything” to the exclusion of field-work I cannot 
understand, for 1 remember more than one passage in which the 
opposite opinion is expressed.’ The two modes of investigation are 
two independent witnesses, and the question is, can there be any 
value in a result founded on the one testimony alone, when an 
investigator, extremely well qualified to interrogate both, has come 
to an opposite conclusion? It is not even as if the two methods 
result in a complete contradiction. It is rather that the rocks at 
Hall Sands form one of those difficult cases where the unaided eye 
can scarcely be trusted. Here we find, alinost in juxtaposition, a 
«schistified ” fragmental rock and a ‘‘fragmentalised”’ schist. The 
question then is, can we draw a line of separation between the two? 
He who relies on field evidence alone may say, I cannot see it; but 
the worker with the microscope replies, There is a clear distinction. 
The positive statement, which is the result of employing the more 
delicate process of investigation, must surely be of the greater 
value; and in such case one could not rely on a hesitating or 
negative answer, which had been the only outcome of the more 
rough-and-ready method. But, in my opinion, even the field 
evidence is strongly in favour of the distinctness of the two series 
of rocks, when we take into consideration the sections, which occur 
elsewhere than at the coast of Hall Sands. ‘The evidence of an 
abrupt change from a crystalline to a non-crystalline rock seems to 
me perfectly clear, not only at Hope Cove, but also along the 
estuary shores north of Salcombe and towards South Pool, and 
inland near Killington. 
I was especially interested, in my first visit to the district, in 
the chlorite schist quarries near Hall Sands,” which are described 
in the article in the Devonshire Transactions; for this occurrence 
of chlorite schist completely disposes of any theory of progressive 
metamorphism. Certainly there can be no gradation from the slates 
of Hall Sands to chlorite schist. But I am puzzled by Mr. Somer- 
vail’s statement that this chlorite rock reappears in the valley “on 
the north of Professor Bonney’s junction, where according to his 
view it has no right to occur.” The chlorite rock occurs to the 
south of the valley, and I do not understand on what grounds it 
is asserted to be north of the junction. Professor Bonney indicates 
the fault by a dash, which necessarily on a map of so small a scale, 
1 Gron. Mac. 1880, p. 299; and 1879, p. 203. 
2 In my map as published in the Quarterly Journal, two lines, which unfortunately 
escaped my notice, have been accidentlly introduced, making it look as if slate existed 
in the Bickerton quarry in contact with the schist. The quarry, as described by Mr. 
Somervail, is entirely of chlorite schist, with slickensided bands, 
