CLiMATOLOGV. 89 



In fact, upon the average of the year the absolute minimum 

 upon the grass is only lower at Alienheads than it is at Bywell 

 by a fraction of a degree. 



Area in North Yorkshire of the Thy-ee Zones of Altitude. — 

 Recurring to our three zones of altitude we must next seek to 

 ascertain what portions of the surface they respectively embrace 

 and what are their characteristic features. The most suitable 

 lines of limit would appear to be the contour lines which mark 

 an elevation of 300 and 600 yards above the sea-level, that 

 portion of the surface which is below 300 yards in elevation 

 being considered as embraced in the Lower Zone, the moor- 

 lands and upper part of the dales which range in height between 

 300 and 600 yards making up the Middle Zone, and the sum- 

 mits of the peaks which rise above 600 yards the Upper Zone. 



On the west the line of an elevation of 300 yards runs from 

 the Tees at Winch Bridge within a short distance of the river 

 as far as the Lune, up the Lune a little, round the edge of the 

 fells above Romaldkirk, ascends Balderdale for a considerable 

 distance, and thence is continued along the edge of Lartington 

 Moor past nearly the head of Deepdale to the Greta near 

 Bowes. From Bowes it curves considerably to the east to skirt 

 the western bank of the dale of Gilling above Dalton and 

 Kirkby Ravensworth, and then turns to the west round Rich- 

 mond Beacon to near the Swale at Applegarth, curving round 

 the lower part of the dale of Marske and again coming sharply 

 down to the Swale in the angle between the main dale and 

 Arkengarthdale. It ascends Arkengarthdale to the foot of Shaw 

 Beck, runs down the west side not far from the Arkle Beck to 

 Reeth Moor and from this point passes due westward not far from 

 the Swale to Muker. South of the Swale it does not leave the river 

 far as we proceed eastward from Muker to Downholme, and from 

 thence it sweeps round the edge of Downholme Moor, Bellerby 

 Moor and Leyburn Moor, runs along within a short distance of 

 the Yore as far west as 'I'hwaite Bridge above Hawes, and there 

 turning again towards the east passes Gayle and beneath Bear's 



June i888. 



