646 PROCEEDINGS UF THE GEOLOGICAL SOCIETY. [June 22, 
south-east. These gravels are well seen in the Blackpool section, 
in the Ribble Cliffs at Red Scar and Balderstone, and in pits near 
Leyland and Chorley. Shells more or less perfect: are invariably 
found associated with these gravels; and in those of Leyland I 
obtained some bones of an herbivorous mammal, which, however, 
were too fragmentary for Mr. Boyd Dawkins, F.R.S., who kindly 
examined them, to identify the species. 
The pebbles in those gravels are all rounded, and are chiefly from 
the Lake-district ; at Leyland and Chorley, carboniferous recks and 
blocks of coal form about 12 per cent. of the larger blocks. With 
few exceptions, these pebbles are never scratched; and both the 
character of the beds, and the species of Mollusca found in them, 
testify to the great amelioration of the climate which ensued during 
the Middle-drift period; this, however, from Mr. Croll’s caleula- 
tions, is only what might be expected. 
In the instances where scratched pebbles occur, especially at 
Samelsbury, the sand is not the clean fine sand usually found in the 
Middle Drift, but has a loamy, or even clayey, character. This 
seems to point to special physical conditions ; and it appears net im- 
probable that during this warm episode in the Glacial epveh stray 
icebergs from regions still further north, or from hills cold from their 
elevation, floated occasionally from the north-west to the south-east 
in the Middle-drift sea. 
Beds of loam varying in thickness from 1 inch to 3 feet occur 
in the Middle Drift; and some of them are much used as sand for 
brass-casting. They generally have a slight dip to the E.S.E. 
These, from having a certain amount of clay in their composition, 
support small sheets of water, which, becoming charged with ear- 
bonate of lime, often consolidate the surface of the loams into a 
substance as hard as rock. This also takes place under exceptional 
circumstances in the gravel-beds, producing masses of conglomerate 
resembling that portion of the Millstone Grit known as the Kinder- 
scont Grit. These are seen in various places in the banks of the 
Ribble and in the Blackpool cliffs, where they are used to form 
rockwork, which has already been described by Mr. Mackintosh in 
his paper before referred to. In many of the deep-brook valleys in 
the Preston district the Middle Drift occupies the sides, and the 
Upper Boulder-clay the top, being separated from one another by a 
seam of this consolidated loam. These seams often run for miles 
without a break, though not more than three inches in thick- 
ness. 
The level of the top of the Middle Drift is an exceedingly variable 
quantity, varying 60 and 70 feet in half a mile, but it invariably dips 
from the hills of the Penine Chain towards the sea and the low 
country. At Blackpool it is 80 feet above the level of the sea, at 
Chorley 275, at Leyland 150; and Mr. Hull gives the elevation of 
the base of the Upper Boulder-clay in “ the valley which runs up 
from Manchester by Bolton to beyond Sharples,” as 275 feet above 
the sea at Pendlebury, at Clifton 285, at Kearsley 300, at Hal- 
shaw Moor 285, opposite Burden Bridge 300, at Bolton 300, and 
