16 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 24, 



3. On the Eoce:-basiks in the Geanite of the Daetmoor District, 

 Devonshire. By G. Warein-g Ormerod, Esq., M.A., F.G.S. 



[Abstract.] 



Ib" this Memoir the origin of E-ock-basins in the Granite of Dart- 

 moor and its vicinity is alone considered ; and it is not attempted to 

 draw therefrom any law as to the manner of the formation of similar 

 basins elsewhere. It has been here attempted to notice all the hol- 

 lows known as E,ock-basins in this district ; and in the table ap- 

 pended, particulars of these and of the chief Tors are contaiaed. A 

 few localities it has not been in the power of the Author to visit ; 

 and the description is in those cases taken from the observations of 

 others : doubtless also some basins have escaped notice, but a con- 

 siderable number have been examined, and the particulars noted on 

 the same system, so as to give an opportunity of comparison. The 

 situation of Dartmoor is too well known to need description. The 

 geological formation is entirely of granitic rocks. From near the 

 same point in the northerly part of the moor the Tavy flows westerly 

 and the Teign easterly : to the north of these rivers very few rock- 

 basins exist, and those too are in the immediate vicinity of these 

 rivers. To the south of a line formed by the Plymouth and Dart- 

 moor railway and the Eiver Dart, it is believed rock-basins have not 

 been found ; but this last district has not been completely examined 

 by the Author. The part of Dartmoor, therefore, in which the rock- 

 basins exist is a central belt, which occupies about one-third of the 

 area of the moor. The particulars of the various basins are set out 

 in a tabular form ; it will therefore be only needful to notice some 

 of the most important. The only basin to the north of the Tavy 

 with which the Author is acquainted is at Hare Tor. To the south 

 01 the Tavy Fur Tor is the highest point of Dartmoor, being 2000 

 feet above sea-level. The rocks composing this Tor are scattered 

 over a considerable area, are much weathered, for the most part 

 broken and low, and forming ledges, but occasionally rising into 

 large masses. The granite is generally porphyritic, being coarse- 

 grained with large felspar, and has a laminated structure. On this 

 Tor there are three basins. Between the Tavy and Wallcombe Eiver, 

 Eoose or Eoll's Tor, Staple Tor, Yixen Tor, and Pew Tor are worthy 

 of notice ; the two last mentioned are particularly described in Bray's 

 Tamar and Tavy. Between Wallcombe Eiver and the East Webber, 

 Mistor is the most conspicuous and known Tor ; it is situate on an 

 insulated hill 1760 feet above sea-level. The Tor consists of long, 

 narrow, low cliffs, which rise on the eastern and western sides of the 

 summit of the hill (that on the eastern side being the most lofty and 

 extensive), ranging nearly from north to south. The space between 

 these is occupied by detached masses varying in size. The granite 

 is laminated and much weathered at the junctions of the beds and 

 of the perpendicular planes, and there are occasionally overhanging 

 beds. " Mistor Pan " is the only basin on this Tor ; it is situate 

 near the northerly end of the eastern range on the summit. This 

 basin has been supposed to be artificially formed, and is described in 



