. Correspondence. 431 
the point, he has I think, proved that I was in error, by finding por- 
tions of the schist entangled in the syenite-trap. 
I know that the last edition of the Geological Survey Map re- 
presents the rocks as altered on the north side, and unaltered on the 
south. There can hardly be this difference. My friend Mr. Hicks 
believes there is alteration on the south side too; so both authorities 
are against me at present. There are plenty of sections, but so 
many cross-faults which require to be allowed for, before even the 
true succession can be established, that I cannot admit that I am 
beaten until the syenite has been thoroughly examined on both 
flanks; and I can only hope good observers will go again and again to 
this interesting point. The last edition of the Survey Map confines 
the syenite to St. David’s and its neighbourhood ; while it makes the 
trap of Ramsey Island a greenstone, similar, I suppose, to that of St. 
David’s Head, and altering similar rocks. We may assume that it is 
a continuation of the St. David’s trap, as I ventured to do in my 
paper. But if the trap and schists of Ramsey Island be really quite 
ditferent from those of St. David’s, opposite, an unmarked fault, N. 
and §., of no little magnitude, must occupy the Sound. The whole 
thing, therefore, wants investigation. Who will doit? Iam quite 
certain, whoever does will have the cordial co-operation of my friend 
Mr. Hicks; and I really have no time to find out my own mistake, if it 
be one. Altered rocks are crotchetty things to deal with; and a sharp 
anticlinal like that of St, David’s does not take place without many 
a parallel fault which may bring the unaltered rock against the 
trap, and deceive others, as it appears to have deceived 
Yours truly, J. W. SALTER. 
On THE FossILs FROM THE SILURIAN SHALES OF Morrat, 
DUMFRIESSHIRE. 
My colleague Mr. Carruthers, and Mr. Young of the Hunterian 
Museum, Glasgow, having called my attention to the communi- 
eation of Mr. Brown (ante, p. 382) regarding his discovery of 
fossils in the Moffat Graptolite Shales, I have, through the kind- 
ness of Mr. Brown, been permitted to examine his specimens. I 
submitted them to Mr. Carruthers, who is acquainted with the beds 
from which they were obtained, and he has supplied me with the 
following notes regarding the fossils and the strata. 
Besides the Graptolites which abound in these shales, there have 
been found two species of a phyllopodous crustacean, Peltocaris, 
described by Mr. Salter in the ‘ Quarterly Journal of the Geological 
Society,’ vol. xix. p. 87, viz., P. aptychoides, Salt., and P. Harknessi, 
Salt. Prof. Harkness has found specimens of the small brachiopod, 
Siphonotreia micula, M‘Coy (Cat. of Fossils in Mus. of Pract. Geol., 
p- 17). Mr. J. Stevens, for some time an enthusiastic explorer of 
the Moffat Shales, discovered asingle specimen of Tentaculites. The 
lighter coloured arenaceous deposits of Hunterbreck Hill contain the 
impressions of Crossopodia Scotica, M‘Coy ; Nereites Cambrensis, 
M‘Coy, and other Annelids (Murchison’s ‘ Siluria,’ p. 199). These 
