527 



EEPOllTS OF THE rROCEEDIN"GS OE GEOLOGICAL 

 SOCIETIES. 



Procerbin'Gs of Tni? Geological Society of Londox. — November 3, 1858. — 

 The following communications were read : — 



1. "On some Natural Pits on the Heaths of Dorsetshire." By the Rev. 0. 

 Fisher, M.A., F.G.S. 



On AiFpuddle Heath and Piddletown Heath, near Dorchester, the surface is 

 pitted with numerous circular or oval hollows, like inverted cones. They usually 

 vary from about 00 to 80 yards in circumference ; but one measui'es 1 80 yai-ds, 

 and another, called ''Culpepper's Dish," is 290 yards round; in the former the 

 sloping sides are 23 yards high ; in the latter 47 yards. After observing that 

 these pits could not have been formed by the washing away of the underlying 

 sand-beds, the author proceeded to show that their formation seemed to be due to 

 the subsidence of the material into ** sand pipes" in the subjacent chalk, owing 

 to the percolation of rain-water containing carbonic acid, which dissolved the 

 chalk ; and Mr. Fisher referred to the explanation of this process given by Mr. 

 Prostwich in a paper formerly read before the Society. 



As this process could have gone on only during a subacrial condition of the 

 surface, and must have occupied a very long time, the author remarks that the 

 larger pits on the Heaths referred to mu^t h ive been formetl by the sinking of the 

 Eocene beds into enormous "sand-pipes" during an extended geological period, and 

 that the area they occupy was dry land during all that time, and has been so ever 

 since, and must, therefore, have formed islands or headlands in Uie sea which last 

 tilled the adjacent valleys, and gave them their present configuration. 



As the formation of these pits was subsequent to the outspread of the superficial 

 gravel of these Heaths, and pi'evious to the last depression and elevation of the 

 land, their date would be, perhaps, near that of the great mammalian fauna. The 

 author also explained his views of the method by which the subsidence of the 

 materials gave rise to the peculiar shape of the pits ; and he observed that some- 

 what similar conical depressions have been noticed in process of formation at the 

 present day. 



2. " Notice of the occurrence of an Earthquake along the Northern Edge of the 

 Granite of the Dartmouth District, on September 28, 1858." By G. VVareing 

 Ormerod, Esq.,F.G.S. 



The shock was slight, and appears to have been confined to a very narrow 

 district, that may be estimated as not exceeding eight miles in width, and running 

 along the northerly edge of Dartmoor, along the line of junction of the granite and 

 the altered carbonaceous rocks. The len;j,th of the area affected by the earthquake 

 is about 21 miles, from Crediton on the east to the Fox and Hounds Inn, on the 

 Tavistock Road, about seven miles from Okehampton. The shock seems to have 

 taken a direction from east to west, to have occurrei about eight o'clock in the 

 evening, and to have lusted, where most severe, about 15 seconds. 



3. " Notice of certain Veins of Granite in the Carbonaceous Rocks on the North 

 and East of Dartmoor." By G. Wareing Ormerod, Esq., F.G.S. 



The following localities are quoted by the author as affording more or less 

 distinct evidence of granitic veins traversing the carbonaceous rocks. Near 

 Meldon, two miles S.W. of Okehampton ; Cocktree Moor ; in the George of the 

 Teign after leaving Hunts Tor ; the most northerly point of Whyddon Park, and 

 the hill-si<Je nearly opposite ; the hill-side above the Logan Stone ; near 

 Wc;'^terly Tor ; on Sharpy Tor; on the road from Cranbrook Castle to Fingle 

 Bridge ; and the ro id down the hill to the wett of Cranbrook Farm. 



4. " On the Struclure of some of the Siliceous Nodules of the Chalk." By N. 

 T. Wetherell, Esq. Communicated by the President. 



The author first described several specimens of the peculiar banded flints found 

 in the chalk and in gravel, and of whicii he had m ide a large collection during 

 several years. They usually exhibit a central longitudinal axis or narrow stem, 



