46  Correspondence—Prof. T. G. Bonney—Mr. A. Somervail. 
for the publication. In the paper on the classification of the Dino- 
sauria, I do not adopt the names given on p. 562; but use the name 
Ornithischia for the order of which Omosaurus is an example, there 
named Omosauria ; while the name Sauwrischia is used for the order 
comprising allies of Cetiosaurus, there named Cetiosauria. I shall 
be glad if this erratum is corrected on p. 562, so that the names 
which appear there may not be quoted, and may be considered not 
to have been published. 
Tue Vine, SEVENOAKS, Dec. 3, 1887. H. G. SEELry. 
DIMETIAN OF ST. DAVIDS. 
Srr,—Mr. Mellard Reade in his paper ‘‘On the Dimetian of St. 
Davids” does not state whether the rock which he found included 
in the “ Dimetian,” and which he calls a “ green shale,” has been 
proved to be such by microscopic examination. Will he kindly 
supply the omission; because, without such an assurance, his proof 
of the intrusive character of the “ Dimetian”’ has no more validity 
than an arch without a keystone. T. G. Bonney. 
PROF. BONNEY ON BANDED GNEISSES AND THE METAMORPHIC 
ROCKS OF SOUTH DEVON. 
Str,—Would you kindly allow me space for reply to Professor 
Bonney’s letter in your issue for December, on the above subjects, 
more especially the latter, which directly affects myself. This 
portion of his letter forms a marked contrast to the other, and at the 
outset I beg to protest against its style and tone, which I shall not 
-condescend to imitate in this reply. 
It is possible or even probable that I may be wrong in my 
interpretation of these South Devon rocks, and if so, on further and 
better proof I shall be as happy in the opposite conclusion, as I 
earnestly trust that I follow science or truth for its own sake. 
With regard to the use of the microscope in geology, let me 
respectfully remind Prof. Bonney that it is not everything. It so 
happens that I too have a stake in the “banded gneisses” of ‘the 
Lizard district, and my field-work there showed me that the whole 
of his “granulitic” group of schists were rocks of true igneous 
origin, a fact forced upon me without the aid of the microscope; and 
further, that the other schists in which the Professor describes 
current-bedding and ripple-drift, etc., etc., I strongly suspected to 
have had also an igneous origin, and these appearances due to very 
different causes, facts which have since been corroborated by a high 
authority. So much for the use and non-use of the microscope, an 
instrument in research which I do not undervalue, and which I mean 
to become better acquainted with. 
Tt is, however, against the tone of the Professor’s letter that I 
complain, and I would invite him (and the rest of your interested 
readers) to compare the portion of it relating to myself with the last 
paragraph of his own article in “ Nature” for November 10th. 
59, Furer Srreet, Torquay, Dec. 15, 1887. ALEX. SOMERVAIL. 
