ELGBE : GLACIATIOX OF NORTH CLEVELAND. 373 
at the outset that the occurrence of large blocks of Augite 
Andesite from the Cleveland Dyke, to the south of its outcrop, 
affords further proof of a northerly ice stream. An exception- 
ally large boulder of this rock stands in a field just south of the 
Dyke at Stainton. At the period of maximum extension, the 
Cheviot Glacier swept right into the angle of the Cleveland 
escarpment, several small lakes being held up along its slopes, 
and overflows existed at Gribdale Gate, the head of Bilsdale, 
Holy Well Gill, and Scarth Nick.* (See Map, Plate LI.) 
These overflows were abandoned with a very slight shrink- 
age of the ice margin, and the impounded drainage would now 
escape along the lower slopes of the Cleveland Hills, but only 
one stream appears to have left any traces of the subsequent 
course of the water. This, the Gribdale Gate overflow, ceased 
to operate at a level of 747 feet, and therefore, the lake im- 
pounded in the hollow of the hills between Roseberry Topping 
and Easby Moor must have escaped either to the north or to the 
south. The overflow at the head of Bousdale. half a mile north 
of Roseberry Topping, discovered by Mr. Kendall at an elevation 
of 675 feet, indicates a westerly flow, and in all probability 
this drainage swept round the hills to Kildale, and was joined 
by the Gribdale Gate waters. No channels are met with proving 
this until we arrive at the 575 foot contour, at Castle Hill, Easby, 
where a small valley exists which will be described later. 
A further retreat of the ice permitted the extra-morainic 
drainage to travel at a still lower level. To this stage belongs 
the deviation of Boosbeck, through the great gorge at Slape- 
wath, which cuts from 600 feet down to 425 feet or thereabouts. 
In alignment with this rock gorge is a channel at the foot of 
Bousdale Hill, near Pinchingthorpe, with a great bank of drift 
(Grove Hill) in front of it, and cutting, at its outfall near Lowcross 
House, the 325 foot contour. Still further to the west, at Lang- 
baurgh, a well-defined overflow crosses the Cleveland Dyke, 
and is certainly in alignment with the Grove Hill channel, since 
the altitude at which it commenced to be eroded is 325 feet, 
the level of the floor of the Grove Hill Valley. The Langbaurgh 
* Kendall, Q.J.G.S., Vol. 48, pp. 513-519. 
