C. E. de Rance—Sections around Southport. 501 
Lonsdale in 1864 (Brit. Assoc. Report), describes the subterranean 
water-ways in the Carboniferous Limestone; these channels are 
locally called “greiks,” and take the whole of the dry weather flow 
of the stream; in floods they have not sufficient diameter to take the 
flow off, which boils down the rocky bed of the stream. The caves 
in the “greik” become gradually enlarged, the roof falls in, and 
the chain of caverns become exposed to daylight and form a steep 
and narrow gorge, but as Prof. Phillips pointed out, the valley is not 
due to the breaking away of the caves; for the valley must have been 
first excavated in the overlying impermeable rocks, before the water 
could have free access to the limestone, and by acting mechanically 
and chemically upon it, have formed the caves. Prof. Hughes points 
out that the condition most favourable to the formation of “swallow- 
holes” and caves is when a deposit of clay, or shale, overlies the 
limestone, and allows the growth of peat, or the existence of decay- 
ing vegetable matter in a swamp, to furnish acid to the water in 
addition to the carbonic acid derived from the air; the limestone is 
always pitted all round the margin of the overlying impermeable 
material, the swallows are initiated at the junction of lines of joints, 
which as the clay is. worn back, determine the existence of other 
sets of swallows. Each set as a rule drains into the same under- 
ground channel far below; so, though the ramifications of the feeders 
vary from time to time, according to the wearing back of the imper- 
meable covering, and the opening out of new swallow-holes, the lines 
of underground drainage remain the same. 
Lower Longridge Grit.—This deposit is the lowest sandstone in. the 
Lancashire Carboniferous series; it is a somewhat inconstant horizon, 
and resembles in character the Gannister beds of the Coal-measures ; 
it is seen in brook sections on the northern slopes of Longridge Fell. 
The Bowland shales of Professor Phillips overlie it, and may be well 
seen in Longridge Fell; and in Parlick Pike, near Chipping, these 
shales form an important part in the scenery of the Forest of 
Pendle, the steep slopes: of which are all composed of the dis- 
integrating shale of this age, reaching a maximum thickness of 
700 feet.. The occurrence of numerous fossils, and seams of iron- 
stone nodules, give these shales the appearance of Ccal-measures, 
which have led to many fruitless searches for coal. 
Upper Longridge Grit.—This is largely worked as a building 
stone in numerous quarries in Longridge, where good sections may 
be seen ; the grit is not less than 1000 or 1200 feet; it is the first 
important member of the wonderful development of Millstone Grit 
occurring around’ the Lancashire Coal-field, which reaches its 
maximum thickness in the neighbourhood of Bacup, and thins south- 
ward to the Biddulph no less than 2000 feet, or about 80 feet per 
mile. The Millstone Grit can be best studied in the Bacup district, 
and around Haslingden. 
The Kinderscout Grit is well seen in the elevated moorland raised 
by faults between the Wigan and Burnley Coal-fields. Good sections 
both of the conglomerate, and of the tine hard beds quarried for 
