304 
DAYKNS : GLACIAL PHENOMENA OF WHARF ED ALE. 
in terraces, like ordinary river terraces. This makes me think that 
there is no real distinction to be drawn between the older river 
gravels and the water-worn gravels with boulders, which are generally 
set down to the glacial period as something quite stti generis. I 
believe on the contrary that the ordinary river gravels run back to 
glacial times, and gradually merge into the glacial deposits. 
I will now consider the solitary case of foreign blocks occurring 
in the valley of the Wharfe. These consist of Silurian Grits like 
some of the Silurian Rocks that occur in places in Ribblesdale. In 
Wharfedale these Silurian boulders are confined to the portion of the 
valley between Chapel House Lodge and Burnsall, that is, all that 
I have met with are below Chapel House Lodge and above Burnsall. 
They are most plentiful about Linton and Threshfield. The greater 
number of them have long since been cleared off the ground and 
built into the walls for " throughs," 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 drift cut through by becks des- 
cending from Threshfield Moor. I could find none above the general 
level of the drift of the more open country, which near Threshfield 
reaches about the height of 800 feet above sea level. I examined the 
country lying between the site of the boulders and the outcrop of 
Silurian Rocks in Ribblesdale ; but though there arc plenty of Mill- 
stone Grit boulders lying on the bare surface of the limestone, not a 
single Silurian boulder was to be found. It was quite clear that these 
Wharfedale boulders had not come over the fells from Ribblesdale. 
Whence and how then did they come ? It may be thought 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 difficulties connected with this view, the chief of which is this : 
if these boulders drifted eastward from Settle on floating ice, when 
the sea level was but little higher thau the present 800 contour line, 
and Wharfedale was a fjord, whether filled with ice or water, how 
did they surmounting the rock barrier at Nether side manage to travel 
up the dale or fjord towards Chapel House ? for assuredly ice, or 
water carrying ice, was flowing down Wharfedale all the while. This 
is an insuperable difficulty to the floating ice theory. 
