374 
ELGEE : GLACIATIOX OF NORTH CLEVELAND. 
overflow presents some features of interest. Just to the west of, 
and parallel to it, is a slight trench in the ridge at 325 feet, over 
which the glacier appears to have readvanced. The over- 
flowing waters then commenced the gap through which the 
Tame flows, and cut down to 275 feet. At the intake of the 
channel, on the north side of the Dyke, is a mound of drift at an 
altitude of 300 feet, in front of which the overflow has clearly 
taken place. The present stream, the Tame, which well merits 
its name, cannot have cut the gap, as further to the west is 
lower country at 275 feet, a clear case of an ice barrier.* 
The fall of these valleys is in consonance with Mr. Kendall's 
observations regarding the overflow at Bushy Dale Wood, on the 
eastern side of the Boosbeck Valley, " v/hich shows that the main 
overflow to which it was related was at a low level, and I feel 
assured that it was into the Vale of York." To summarise the 
altitudes : Bushy Dale, 600 feet ; Slapewath, 600-425 feet ; 
Grove Hill, 450-325 feet ; Langbaurgh, 325-275 feet. 
A retreat of the ice, when Slapewath had been cut down to 
about 425 feet, enabled the waters of Boosbeck to flow to the 
sea at Saltburn, and this explains the fact that no dry valleys 
have been eroded on the northern slopes of Airy Hill, for when 
the ice-front was standing on that hiUside the drainage was 
travelling down the Guisborough Valley. 
A series of channels occurs at the foot of the Cleveland 
Hills which belongs to an earlier stage than the preceding, and 
which may, judging from the altitudes, hav^e carried the extra- 
morainic drainage from the Boosbeck Valley for a brief period. 
These valleys, however, do not seem to form an aligned sequence, 
but ratlier appear to be due to lobes of ice standing on or 
behind drift mounds, and allowing the drainage of the slopes to 
sweep between them and the hill sides. The Grove Hill channel 
is one of these (Plate LII.). Near Great x\yton Station we 
find a great mound of drift at 450 feet, with a channel between 
it and the steep hillside. It is nearly 50 feet deep and falls 
southwards (Plate LIII.). 
* The Tame is mostly artiticial, consisting of drainage channels for 
the formerly swampy Guisborough Valley. 
