Notices of Memoirs—James Thomson on a Coral Atoll. 549 
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James Taomson, F.G.S., on a Fosstn Conran Aront on THE SHorE 
Line at ARBIGLAND, NEAR Dumrrizs, Scornanp. 
Abstract of paper read before the British Association, Southport Meeting, 1883. 
(Section C, Geology.) 
bl ‘author briefly described the stratigraphical position of the 
rocks on either side of the Solway Frith, and stated that the 
centre of the Solway was a line of depression or fault, that the series 
of rocks to which he wished to refer belonged to the lower members 
of the marine series of the Carboniferous system. In all the sections 
that he had visited he found the beds dipping at various angles 
inwards and downward on either side of the Frith, and referred 
to the abundance of the coralline remains in many of the sections he 
had examined along the shore-line. 
The rocks on the shore at Arbigland consist of Limestone bands 
belonging to the lower members of the Carboniferous Limestone 
Series. The lower bed is exposed along the shore-line as a linear 
reef for about two miles, and is largely composed of corals of 
several genera and species. The Limestone along the inner margin 
becomes more or less arenaceous, and passes into a calcareous shale, 
largely composed of marine exuvie. Imbedded in this shale are 
a series of dome-shaped masses of Zithostrotion of varied species. 
These beds are overlaid by another band of limestone, which is also 
composed of species of corals around the inner margin, the conditions 
are similar to those of the former beds, the dome-shaped masses also 
belong to the genus Lithostrotion, but belong to different species, and 
the matrix is largely composed of similar forms of coralline remains. 
The next reef becomes more or less circular, and is overlaid by 
a series of reefs, all more or less composed of coralline remains ; 
the outer marges of the reefs recurve and present an open face 
to the south. Here the domes of coral assume gigantic proportions. 
While around the inner portion of this reef the domes are smaller 
on the whole, they vary from an inch up to eleven feet in diameter, 
and consist of many species. The series from this, inwards to the 
centre, consists of twelve successive reefs, all circular in outline, and 
composed of limestone with interstratified shale, all more or less 
made up of corals of varied genera and species. The inner of these 
reefs is circular and more conspicuous, and 240 feet in diameter, it 
passes from a compact limestone, made up of coralline remains, 
into an arenaceous shale, in which are imbedded numerous domes of 
corals and other marine exuvie, the centre of this circular reef is 
filled up with calcareous sandstone. The entire series of these 
semicircular and circular reefs is 2976 feet in diameter, and dipping 
at angles varying from 12° to 15° inwards and downwards, which, 
from calculation, implies that the water inside the original reef was 
about four hundred feet deep. A mile to the east there is another 
series of circular reefs; these, however, dip outwards, fold round 
and clasp a central mass. On the whole we thus have exposed 
