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THE GEOLOGIST. 



pendicular joints clearly developed, the angles where exposed being 

 only slightly weathered, and the horizontal beds, if thick, standing 

 out with well-defined edges and ends ; if thin, with sharp projecting 

 edges, giving to the side a serrated appearance, rock-basins are 

 scarcely ever found. When, on the contrary, the tor is rounded, the 

 sides sloping or smooth, projecting beds not frequent or bold, and 

 such beds as do project for the most part rounded at the edges, 

 rock-basins will very frequently be found. For the above reasons 

 Mr. Ormerod considers that in this district the rock-basins were 

 caused by atmospheric action, that power working gently but surely 

 upon the rock, and equally forming every description of basin, be 

 it large or small, deep or shallow ; this he considers the rotation of 

 pebbles could not do. 



The direction of the longest diameter is in nearly one-third of the 

 cases from north to south, and in all but five out of the thirty-five 

 cases is from the north-westerly to the south-easterly quarter : the 

 cause of this Mr. Ormerod has not been able to discover. Although 

 the direction of the longest diameters is in the greater number of 

 instances towards the points, between which the perpendicular joints 

 of the granite of Dartmoor generally range, he has not found that 

 there was any connexion between them, the direction of the longest 

 diameters rarely corresponding with that of either the main or cross 

 joints on the same tors ; neither do the directions of the basins on 

 the same tor always agTee. The most violent storms on Dartmoor 

 come from between west and south-west ; although occasionally 

 heavy gales occur from the south-east, the winds from between the 

 south and east are generally mild, and those between the north and 

 north-west are not of frequent occurrence. The direction, therefore, 

 of the longest diameter cannot be assigned to the action of the 

 strongest or most prevalent winds." — Quarterly Journal Geol. Soc, 

 vol. xiv., pages 22, 23. 



