58 
BRITISH ASSOCIATION.- 1835 . 
veins are frequently observable, such as their passage through the 
adjacent schists, detached portions of which are often enveloped 
in their substance, and the change they effect in their structure. 
Mr. Griffith next described the older and newer trap districts, men¬ 
tioning many interesting particulars connected with them, such as the 
capping of quartz rock by greenstone, the concentric arrangement 
of the beds of greenstone in Donegal, and the occurrence of quartz 
rock between two beds of greenstone, the quartz being columnar, 
the trap, above and below it, not. In Slieve Guilin greenstone and 
granite were stated to be actually mixed together, whilst in Carling- 
ford the contact of the sienite (or greenstone) with the granite is 
concealed by debris. After noticing briefly the ochre beds which 
so often separate the beds of basalt, and expressing his belief that 
the trachytic porphyry of Sandy Brae in Antrim was nothing more 
than this ochre indurated by heat, Mr. Griffith adduced the fact of 
beds of sienite traversing the cliffs of Murloch Bay, and containing 
detached portions of chalk, as proof that the sienite was posterior 
in appearance to the chalk; and gave it as his opinion that all the 
crystalline rocks had been fused, and in most cases projected from 
beneath through the sedimentary rocks, the appearance of regular 
strata being due to their projection in a direction parallel to the 
strike of the beds. 
Mr. Griffith stated the existence of an extensive marl deposit in 
Wexford, some of the shells of which appeared to correspond with 
those of the crag. 
On a small isolated Patch of Granite which occurs in the County of 
Cavan. By Lieutenant Stotherd. 
The superficial extent of this granite is about seven square miles, 
and it is separated from the nearest group of primitive rocks, that of 
the Mourne mountains, by the grauwacke or transition schists. This 
small district is entirely surrounded by transition and secondary 
rocks, and exhibits all those changes in the structure of the sedimen¬ 
tary rocks which are usually observed on their approach to, or con¬ 
tact with, rocks of a decidedly igneous origin, the schists becoming 
indurated and often changed to quartz rock. The appearance of 
primary rocks so far removed from any of the greater masses is 
extremely important in geological speculation, and assists in this 
instance in explaining the broken and detached character of the 
schistose hills, and the induration of many of their strata, since it is 
probable that the granite is at no great distance from the surface 
in the whole space between the Cavan primary rocks and the 
Mourne mountains, of which they may be considered an extension. 
Copies of a map of the geology of the environs of Dublin, accom¬ 
panied by a memoir, were presented to the Section by Dr. Scouler, 
Professor of Geology to the Royal Dublin Society. 
