50 REPORT—1843. 
On the occurrence of a Bed of Sand containing recent Marine Shells, on the 
summit of a Granite Hill, on the coast of the county of Mayo. By Ricuarp 
Grirritn, F.G.S., §c. 
The peninsula called the Mullet of Erris, is situated to the west of Broad Haven 
and Blacksod Harbour, on the north-western coast of the county of Mayo. Its length 
is fifteen miles, breadth on the north five miles, and on the south two miles. e 
northern portion presents some hills of moderate elevation, the most important being 
Aughalasheen, which reaches the height of 434 feet. The central part of the penin- 
sula, though not absolutely flat, is low and uninteresting, the principal elevation not 
exceeding 120 feet, the average varying from twenty to sixty feet above the level of 
the sea. At the southern extremity, the only striking elevation consists of Termon 
Hill, whose summit is 342 feet above the level of the sea. 
The rocks of which this peninsula is composed consist of quartzite, mica-slate, 
metamorphic mica-slate, passing into gneiss, hornblende slate and granite. The 
quartzite occurs at the northern extremity, and forms the conical hill of Augha- 
lasheen. ‘The principal tract of mica-slate is situated to the north of the village 
of Belmullet, to the south of which it exhibits a highly crystalline and metamorphic 
structure, and the strata present alternations of gneiss with large crystals of felspar, 
gneiss passing into hornblende slate, and sometimes porphyry ; the beds are not thick, 
but frequently present a tortuous arrangement. The metamorphic strata extend to 
the southward from the parallel of Belmullet to the south of Elly Bay, a distance of 
seven miles, where mica-slate again commences, and continues to the base of Termon 
Hill, which is composed of highly crystalline gray granite, arranged in very large 
tabular masses, which affect a nearly horizontal position: some of these masses as- 
sume arhomboidal form, others are slightly wedge-shaped, but neither in the external 
aspect nor internal structure do they exhibit appearances of a stratiform arrangement ; 
in fact they are precisely similar to the tabular-formed granite of Slieve Donard, and 
other granite mountains in the county of Down. 
On the shore at Portglash, at the north-western base of Termon Hill, there is a 
very fine junction of the granite with metamorphic mica-slate passing into gneiss. 
The division of the two rocks at the point of contact is quite clear and well-defined, 
without the least appearance of gradation or passage of one rock into the other. In 
some places the two rocks do not adhere, the gneissose rock being slightly distinte- 
grated near the contact, in others angular fragments of the schistose rock are en- 
veloped in the granite. There are only a few small granite veins penetrating the 
slate, which are composed of felspar, quartz and mica, with interspersed garnets, 
which are abundant where the veins become narrow near the termination. 
To the south of the junction the schistose rock forms a narrow band between 
the granite and the sea, along the west coast for the distante of a mile and a half. 
In some parts this metamorphic rock is much more crystalline than in others. Where 
most crystalline, the rock is composed of felspar in small grains, with much black 
mica, which is arranged in parallel layers, and the general structure of the rock is 
stratiform, but the great lines of stratification are nearly obliterated; but this rock, 
though it assumes a granitiform appearance, bears no resemblance to the true white — 
granite close to it, or to the granite veins by which it is penetrated. © 
A considerable portion of the surface of the peninsula of the Mullet is covered by 
a vast accumulation of white siliceous sand, containing a great number of recent 
marine shells, and on the surface some land shells. The varieties found consist of 
Purpura lapillus, Littorina rudis, Patella vulgaris, Cardium edule, Mytilus edulis, 
Littorina littorea, Ostrea edulis, Pecten varians. 
On the west coast of the centre of the peninsula, particularly to the north and 
south of Elly Bay, the surface of the country is covered by this sand, which is re- — 
gularly stratified in thin layers, and which forms considerable hills, varying in height 
from fifty to eighty feet, the whole being formed of sand, without any admixture of 
mud. 
The marine shells are scattered throughout the mass, but appear to be most 
abundant near the base. 
In those positions where the sand has been blown away so as to form valleys 
among the sand-hills, the surface is thickly strewed with both marine and Jand 

