Pe ee ee ee ee 
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TRANSACTIONS OF THE SECTIONS. 61 
never developed to'a thickness greater than fifty feet in the south of theisland. This 
conglomerate ‘seems to pass regularly into the superior dark limestone by a gradual 
abstraction of the larger quartz pebbles and the substitution of a brownish carbona- 
ceous paste in place of the previous ochreous and gritty matrix. The characteristic 
fossils of these lower dark limestones are Orthis Sharpei, Leptena papilionacea, Phillip- 
sia Kellii, a Creseis and Posidonia, with abundance of the larger corals and Producte. 
Some sudden change, however, appears after a time to have taken place in the 
physical condition of the basin, probably by an elevation of the sea-bottom, for the 
dark limestones are at once replaced by a series of light-coloured beds without shale, 
and abundantly charged with fossils which coincide with those of the lower scar 
limestone of Yorkshire, the dark limestone fossils resembling those of the lowest 
Northumbrian shales and of Hook Point in the south of Ireland. These light- 
coloured limestones attain a thickness of rather more than fifty feet. There is evi- 
dence again of another very sudden change having taken place in this area owing to 
a disturbance, accompanied with an outpouring of trap, along a line from the Stack 
of Scarlet to the hill above Balladoole ; and subsequently, for some time, deposits 
of volcanic ash were constantly being accumulated in this area, and along with them 
the regular carboniferous deposits of this period were developed. This formed a 
trappzan limestone; and when at one particular period a quiescence of the volcanic 
eruptions took place, the bed of Posidonia schist which forms the marble quarry at 
Poolvash was deposited. 
Another eruption broke up this bed, carrying along with it fragments which are 
mingled with the trap, so as to form a breccia; and subsequently the whole mass 
appears to have been subjected to considerable heat, and has suffered disturbance, 
being traversed by trap-dykes which intersect the area in directions generally north- 
west and south-east. 
The author then noticed some remarkable bosses on the surface of this area, both 
in Poolvash Bay and elsewhere. The origin of them he attributed to the intrusion 
of trap amidst the old red conglomerate betwixt the schists and the tough lime- 
stones, 
_ He then observed that the greater part of this southern basin of the Isle of Man 
was covered up by masses of boulder-clay and by an accumulation of diluvium ; and 
he proceeded to some notice of the direction in which the materials appear to have . 
been moved into the locality where they now are. He directed attention to two 
slabs obtained from Poolvash Bay and Scarlet strongly marked with parallel groovings 
and scratches, in directions east-north-east and west-south-west, and he accounted 
for them by observing that at the period of this formation the present Isle of Man 
“was divided into three islands, and that most probably, through the channels between 
them, currents would run, as at the present time, between the Calf of Man and the 
main island. Icebergs drifting along through the southern channel, and carrying 
with them hard pebbles and blocks of the harder limestones, in passing over their 
basset edge, which lies to the north-east of Castletown Bay, would score and polish 
every more eminent flat surface exposed in the channel as those at Poolvash and 
Scarlet. The shales would form abundantly the clay of the period. By a compari- 
son of the contained rocks, he showed that the drift-current came from the east- 
north-east ‘and not from the west-south-west. ‘The overspreading diluvium appears 
_ to have come in quite a different direction, viz. from the north-west, bringing down 
_ rolled blocks of granite of South Barrule. It contains also, amongst other travelled 
_ rocks, chalk-flints, which must be referred for their origin to the north of Ireland. 
