194 JOWETT AND MUFF I GLACIATION OF BRADFORD, ETC. 
extends from below Skipton to the western outskirts of 
Leeds, and is bounded by the Aire and Wharf e divide on 
the north, and by the Aire and Calder divide on the south. 
The following is a brief resume of the chief results 
obtained by previous observers in this district : — 
In 1869 Taylor* described the gravel mounds occurring 
in the Aire valley, near Bingley, and concluded that they 
were formed during a " pluvial period," when the River 
Aire had a much greater volume than it has at present. 
Macintoshf in 1871 mentioned the distribution of super- 
ficial deposits of boulder-clay from the north-west of Aire- 
dale to the east of Leeds, and remarked that the Carbon- 
iferous Limestone pebbles and boulders contained in the 
clay are very abundant in the north-west, but decrease in 
numbers south-eastwards. Although leaning towards deposition 
in water as an explanation of the facts, he very carefully noted 
the difficulty of separating the various deposits — clay, sand, 
and gravel — into distinct strata. 
In 1872 the following important generalisations were 
arrived at by Mr. Dakyns.J The ridge between Airedale 
and Calderdale separates the former drift-covered area 
from the latter driftless one. Wherever two large valleys 
join there is a great pile of drift heaped up between 
them. Where a barrier of rock crosses the valley the 
drift is piled up in mounds against and over the rock, and 
above such a barrier there is a wide spread of alluvium. 
The nature of the drift, and the fact that it is generally 
found entirely on the east and south-east sides of hills, 
indicate that the direction of ice-movement was generally 
from west and north-west to east and south-east. 
Besides water- worn gravels the occurrence of "scratched 
gravels " was recognised, and their passage into water- worn 
gravels noted. 
* Quart. Joum. Geol. Soc, vol. xxv., 1869, p. 57. 
fProc. Yorks. Geol. and Polyt. Soc, vol. v., 1871, p. 103. 
X Quart. Journ. Geol. Soc, vol. xxviii., 1872, p. 382. 
