130 
COLE I ORIGIN AND FORMATION OF WOLD DALES. 
rainfall on the Wolds is rather to fill up existing valleys, by 
carrying down the steep sides a certain amount of loose 
material, and leaving a talus at the bottom, added to other 
reasons which will appear in the sequel, entirely preclude the 
idea. 
It will be well however at starting, to add somewhat, by 
way of description, to the sketch map, which only presents to 
the eye the connection and ramification of the dales in the 
area selected. 
The dales have a uniformly level surface at the bottom, 
varying from a few yards to upwards of 100 yards. The 
bottoms are mostly composed of a cherty gravel, which in- 
creases in thickness as the dale approaches the sea level ; but 
in some, and notably in Thixendale, the bottom consists purely 
of [Kimmeridge] clay ; the chalk having been cut through 
to its base. The sides are truly sinuous, and correspond in 
this respect — that wherever one side is concave the other is 
convex : but as a rule, and as might be expected under any 
theory of excavation, the concave side is the steepest. 
The steepness varies considerably, from 10 degrees to 
nearly 40 degrees. The opposite sides are in many instances 
of the same elevation, and rise at the same angle ; but it 
frequently happens that where one side rises abruptly the 
other has such a long gentle slope that the features of a true 
dale are almost lost. As a rule the steepest sides face the 
north and west. This is well exemplified in the dale leading 
from Burdale to Thixendale, round to "VVayrham; also in 
Yorkdale, leading from Fimber Station to Sledmere. 
The depth also varies considerably, from 30 feet up to 
200 feet. The level of the bottom rises by a gentle slope 
upwards for a distance of some miles, but increases rapidly 
towards the termination as it reaches the tableland. 
On the sides, and at varying elevations above the bottom, 
are found here and there beaches, or beds of gravel, composed 
