1896.] the Plateau Gravel of Salisbury and elsewhere. 123 



Tertiary beds, and boulders of various far-travelled rock which 

 had got distributed over the surface by earlier operations, not 

 always easy to explain after so many changes have taken place. 



It is from one of these patches of gravel, resting on a bed 

 of sandy loam of Tertiary age, at Alderbury, three miles south 

 of Salisbury, that most of the flints I now lay before the Society 

 in illustration of my paper were procured. Some of them were 

 collected and given to me by Dr Blackmore, who kindly drove 

 us to the locality and gave us much information about the district. 

 I exhibit also some of the Kentish palreotoliths of Prof. Prest- 

 wich and Mr Harrison, kindly lent by Mr Fisher, and some 

 collected by myself, near Cambridge. The flints and fragments 

 show evidence of having been long exposed on the surface. The 

 sandstones are often fretted and eaten away rather than rolled. 

 Some of the flints have a good coating of soft white silica, from 

 which the more soluble colloidal portion has been removed, and 

 they exhibit traces of the innumerable accidental chippings and 

 crushings and breaking up under the influence of frost and sun 

 to which surface-flints are liable ; while some were deeply stained 

 by dark red oxide of iron when buried in the gravel into which 

 they had found their way after they had been long knocked about 

 and chipped and weathered on the surface of the ground. 



It was clear that the particular beds we were examining were 

 not merely a surface soil formed in place, but a violently trans- 

 ported drift from a chalk surface covered with weathered flints, 

 such a deposit in fact as would be carried down a slope of chalk in 

 storms when the rainfall was greater than the soil could absorb, 

 and ran off in torrents, tearing up the rubbly disintegrated chalk 

 and hurrying along the surface soil and flints. In such a case 

 a chalky gravel is formed with irregular beds of fine marl, the 

 matrix being almost entirely made up of chalk. When this is 

 afterwards exposed to the slow decomposing action of percolating 

 waters and the carbonate of lime is carried away, only the in- 

 soluble flints and sand and iron oxides remain. 



Of this we see distinct proofs in the Alderbury beds. The 

 flints did not all lie as they would in an ordinary river-gravel 

 with their longer axes horizontal or so inclined as to enable the 

 mass to offer best resistance to the current, but they were fre- 

 quently arranged vertically in loops and hollows into which they 

 had sunk owing to the gradual but irregular removal of the in- 

 cluded masses of chalky material. 



In one place I observed that a part of the chalky matrix had 

 been banded by infiltered iron oxides, so that the iron ran in 

 wavy lines conforming to the outline of the included fragments. 

 When the calcareous portion was dissolved away, those stood 

 out in separate septarian bands of iron oxides. 



