Geological Society. 319 
bed of the sea, of the period of eruption alluded to, have been obli- 
terated by subsequent denudation; and I may suggest that this cause 
has often prevented geologists from recognising the analogy of 
trappean phzenomena to those of submarine and insular volcanos 
now active *. 
In another communication Mr. De la Beche informs us that the 
“ Cornish grauwacké,” in which term he here comprises the slates 
of that country and their associated sandstones and conglomerates, 
contains in some places organic remains. Specimens of these fos- 
sils have been presented by him to our museum. He also states 
that this greywacke formation, which extends into Somerset and 
Devon, is older than Mr. Murchison’s Silurian system, and may be 
subdivided into natural sections, coinciding perhaps with some ob- 
served by Professor Sedgwick in the Cambrian group. ‘The slates 
of Tintagel, long since known to be fossiliferous, belong to the same 
age as this greywacke of Cornwall. 
A joint paper by Professor Sedgwick and Mr. Williamson Peile 
has made us acquainted with the carboniferous limestone flanking 
the primary Cumbrian mountains, and with the coal-fields of the 
north-west coast of Cumberland. These carboniferous strata rest 
unconformably on the primary Cumbrian slates. The carboniferous 
series is divided into four groups: Ist, The great scar limestone; 
2nd, Alternations of limestone, shale, and coal; 3rd, Millstone 
grit; 4th, Great upper coal formation. It appears that the struc- 
ture of the carboniferous limestone is nearly the same as that of the 
Yorkshire chain so admirably described by Professor Sedgwick in 
the first part of our fourth volume just published. 
Mr. Griffith, who has for so many years been preparing a geologi- 
cal map of Ireland, has described to us the position of some veins of 
syenite which traverse the mica-slate and chalk near Fair Head in the 
county of Antrim. The syenite is composed of dark green erystal- 
lized hornblende and brownish red felspar, with occasional grains of 
quartz ; and the chief point of interest consists in the circumstance 
that the syenitic veins have the appearance in general of being regu- 
lar beds in the mica-slate, being for the most part conformable both 
in strike and dip. They are found, however, when more closely 
examined and traced for some distance, to deviate from the strati- 
fication of the mica-slate, and to have an indented and saw-like edge 
at their junction. Similar syenitic veins also penetrate through the 
chalk in the neighbouring part of the coast, and near their contact 
with the chalk nodules or spheroidal masses of syenite are occa 
sionally observed so isolated and surrounded by chalk that had not 
the intruding veins clearly proved its posteriority, the syenite might 
be mistaken for the older rock, rounded fragments of which had 
been imbedded in the calcareous stratum. These phanomena 
remind us of the isolated nodules of granite which in Cornwall, 
the Valorsine, and other countries, occur in the immediate vicinity 
of granite veins. 
* (See on this subject Lond. and Edinb. Phil. Mazg., vol. vii. p. 515.] 
