20 
in determining the direction of the various streams. The 
river study is naturally very closely linked with a knowledge 
of the structure and position of the hills. In this respect 
it may be readily seen that the Calder basin is naturally 
divided into two parts by a line which runs almost east and 
west. This line may be drawn from east of Laneshaw Bridge 
to the Read end of the Whalley Gorge. On the north of 
this line the millstone grit ridges and vallys succeed each 
other in order ; on the south are the wide moorlands and 
carved valleys of the middle and lower coal-measures. It 
is quite plain that the line roughly follows the boundary of 
the coalfield, and that the district is very different structurally 
on the two sides. The long parallel ridges of hills on the 
north side are in sharp contrast to the great blocks of moor- 
land on the south side, separated into semi-detached masses 
by such rivers as the Don, Brun, nad Burnley Calder. At 
present the main structural stream is the one which extends 
longitudinally right through the basin, and which follows 
the Colne Water or East Calder. There is little doubt that 
there was once a very similar longitudinal stream which 
occupied the long valley in the middle of which Sabden is 
situated. Rising on the south-western slopes of Weets and 
the hills above Admergill, this stream would run right along 
the valley of the Sabden Shales across the present junction 
of Pendle Water with the Calder, and would join the then 
Calder somewhere farther out towards the end of the laternal 
branches of the Pennines. This stream has been beheaded, 
however, by a stream which cut rapidly back from Higherford, 
and which eventually collected together the drainage of a 
large part of that longitudinal valley, add also of the incipient 
similar valley just in front of Pendle, Twiston Moor, and 
Burn Moor. The middle portion of Pendle Water may be 
taken as a good example of a longitudinal stream, while the 
lower portion forming the beautiful gorge, partially blocked 
by glacial deposits, between Watermeetings and Higherford, 
is a transverse stream. 
Pendle Water, of West Calder, is a very vigorous river ; 
it falls from a high elevation to less than 400 feet in a com- 
paratively short distance, and so its cutting and carrying 
powers are both great. 
The great system of rivers on the south side is quite different 
in its characteristics. There the rivers are gradually wearing 
their way down into the slightly inclined strata of coal- 
measures and millstone grits, and are thus dissecting a table- 
land into a number of detached masses. The Don, Swinden 
Water, the Brun and the Burnley Calder all drain portions 
