147 
prominences or ground-out hollows irrespectively of the 
structure of the rocks, or undermined pillars so as to leave 
the upper parts projecting. On Brimham Moor, many of 
the most striking pillars are close on, or near to, the verge 
of high cliff-lines, and they have undercut sides facing 
directions from which wind charged icitli sand could never 
have assailed them.* 
Origin of Valleys and Outlet Gorges. — Professor 
Phillips long ago noticed the extent to which the con- 
tours of the valley-systems of Yorkshire were independent 
of the direction of the drainage, and no unbiassed observer 
can make a survey of the hilly districts of the West 
Riding without seeing that fresh-water drainage could never 
have excavated the principal valleys. In these districts 
there are innimierable valleys which cross watersheds, vary- 
ing in depth from a few yards to more than a thousand feet. 
Though small streams flow down both ends of these passes, 
they may be called riverless valleys, and the amount of 
excavation in the middle, where no streams exist, has gene- 
rally been greater than towards the two ends — that is to say, 
the sides of the passes rise highest in the middle. The passes 
between Skipton and Bolton, and between Skipton and 
Pilston, may be taken as average examples. It would be 
little else than a waste of words to endeavour to show that 
these valleys could never have been excavated by fresh- 
water streams. What are called river valleys are here and 
there connected by riverless valleys, and on examining one 
of these valleys — the valley of the Aire, for instance — we find 
that it consists of a number of valle3^s pointing in various 
directions. Across rather than along these vallej^s the rivers 
flow. The valleys have a contour independent of the channels 
* Professor Ramsay's suggestions to Mr. Green, relative to the undercut mill- 
stone-grit pillars on the High Peak table-land, will not apply to the Brimham 
Bocks. 
