DAKVNs : (;la('ial phknomkna of WHAHFKDALK. .')/ 
House Lodge, and they do not extend quite as far as Burnsall. 
They are most plentiful about Linton and Threshfield. The 
o^reater number of tliem have lonp: since been cleared off the 
ground and built into the walls as " tliroughs," where their 
remains may still be seen ; but some few I found still lying 
about on the surface of the land ; and some may be seen in the 
section cut through tlie drift by becks descending from Thresh- 
field Moor. I could find none above the general level of the drift 
of the more open country, which near Threshfield reaches tlie 
height of 90() feet above sea-level. I examined the country 
between the site of the boulders and the outcroj) of Silurian 
rocks in Ribblesdale : but though there are ]:>lenty of Millstone 
Grit boulders lying on the bare surface of the limestone, not a 
single Silurian boulder was to be found. It is quite clear that 
these Wharfedale boulders did not come over the fells from 
Ribblesdale. It may ))e thouglit at first sight that they came 
on floating ice discharged from a glacier debouching at the 
mouth of Ribblesdale near Settle. But there are great difii- 
culties connected with this view, the chief of whicli is this : 
If boulders drifted eastward from Settle on floating ice when the 
sea level was but little higher than the present 900 feet contour 
line, and Wharfedale was a fjord, how did they, surmounting 
the rock-barrier at Xetherside, travel up the dale or fjord 
towards Chapel House ? For assuredly ice, or water carr>dng ice, 
was flowing down Wharfedale all the while. I believe the true 
explanation of the origin of the boulders to be this : At the 
foot of Kilnsey Crag strong springs break out from the limestone 
just above the level of the alluvium ; also in Littondale strong 
springs break out at the foot of the limestone scars, the hillside 
below being formed of a mass of detritus, which as completely 
conceals the underlying rocks as does the alluvium at Kilnsey. 
Seeing then that strong springs break out at the foot of 
scars formed by limestone of great thickness, and that it is only 
at a short distance below the springs that we begin to find Silu- 
rian boulders in the dale, it seems likeh^ that the springs are 
thrown out by Silurian rocks in place in the bottom of tlie 
