/. C. Mansel-Pleydell — Geology of Dorset, 443 



The blocks of Grey Wethers, Sarsen Stones, or Druid Stones, which 

 are scattered over the surface of the Chalk and older formations, 

 such as the saccharoid sandstone of Portisham and Bridehead valleys, 

 or the red sandstones at Winterborne Whitchurch, Milborne St. 

 Andrew, etc., are thought by Mr. Prestwich to belong to the Wool- 

 wich and Eeading Beds. Near the village of Broadmayne on the 

 Wareham road are several blocks of indurated masses of sandstone 

 (Druid Stones) in situ, left denuded by the force which scooped out 

 the valley. The Portisham and Bredy breccias differ, inasmuch as 

 they are conglomerates of flint, and transported from their original 

 position by torrential action into these deep valleys. 



London Clay. — Immediately resting on the Woolwich and Eead- 

 ing Beds is the basement-bed, as tei-med by Mr. Prestwich ; it is 

 usually composed of ferruginous brown clayey sands. At East 

 Bloxworth it contains nodular concretions of clay-ironstone, peroxide 

 of iron, and rounded flint-pebbles : it is a constant attendant of the 

 Woolwich Series in the county from Chalbury to Knighton, but is 

 absent on Piddletown Heath and the outliers westward to Blackdown. 



Middle Eooene. — Lower Bagshot. — These beds consist of a thick 

 deposit of sand and clays ; they are extensively developed on the 

 eastern side of the county, forming the main portion of the clay and 

 heath district included within the Poole basin. They are remarkable 

 in Dorsetshire for their important strata of pipe-clay, which is worked 

 at Creech Grange, Nordon, and Eempstone. The export of this clay 

 in 1870 from Poole was 60,210 tons. Mr. Prestwich considers the 

 Lower Bagshot series, both in Hampshire and Dorsetshire, to be 

 derived from the wear and denudation of land consisting of the 

 older and crystalline rocks ; the condition of the material being 

 similar to rocks such as now form the strata of Cornwall and 

 Brittany. Mr. Maw, however, thinks that these beds have been 

 derived from the denudation of a Chalk- tract. The grains are larger 

 and coarser at Poole and Studland than in the Isle of Wight, where 

 they pass into grits. An old land seems to have existed, of which 

 Cornwall and Brittany remain, the intermediate portion having been 

 submerged and destroyed ; the fossil remains point to the same 

 conclusion, for the plants they contain are more numerous and 

 better preserved as we proceed from east to west, and become more 

 plentiful at Bournemouth, Studland, and Poole than at Alum Bay. 

 In the compact clays of these localities there are not only Dicotyle- 

 donous leaves but numerous fronds of ferns allied to Gleichenia, 

 which are well preserved, with their fruit, a genus which existed in 

 the Cretaceous and Oolitic periods and now inhabits the Cape of 

 Good Hope and New Holland. In the midst of these leaf-beds, in 

 Studland Bay, freshwater shells of the genus Unio attest the fresh- 

 water origin of the white clay.' The fruit of a member of the Arelia 

 family, now confined to North America, New Zealand, Japan, and 

 the East, has been found at Bournemouth by Mr. Mitchell. Fine 

 specimens of the leaves of a Palm (of the genus Sabal) have been 

 found at Studland and Corfe. The river of that period may have 

 1 Lyell, Student's Elements of Geology, 1871, p. 238. 



