part 4] JURASSIC cheonologt. 421 



Mr. Linsdall Eichardson has said that the Burton White Bed is 

 in situ in Bridport Sands formed by percolation subsequently ^ ; 

 but while such an explanation might account for a deposit, it is 

 quite inedaquate to account for the presence of fossils . in that 

 deposit. It seems hardly sufficient to account for such a deposit 

 as this : percolation should produce calcite- veins (the so-called 

 'beef'), not a finely-laminated lithographic stone. The difficulty 

 about the fossils in the deposit Mr. Kichardson avoids hj a sugges- 

 tion which ignores my statements, and is totally at variance with 

 the facts ; he saj^s : 



' It was probably from this horizon [the top of the Red Beds] that the piece 

 of " lithographic " stone came that yielded to Mr. Buckman fossils indicative 

 of late niortensis or garantiangs hemera. Prof. S. H. Reynolds has very 

 kindly examined microscopically one of the two pieces of "lithographic" 

 stone that Mr. Buckman gave to the Director [Mr. Richardson], These two 

 particular pieces probably come from the top of the Red- Bed horizon.' ^ 



My statements were 



' The White Bed .... only occurs .... in the bank at the beach opposite the 

 villas .... It is particularly exposed on the sort of pathway leading from the 

 road to the beach, and ' just to the right hand as one reaches the beach. . . . 

 The blocks on the beach were broken. The yield was several specimens [of 

 fossils] .... and a piece of a Garantiana sp. nov, . . . known as a species from 

 the niortensis beds of Louse Hill, near Sherborne.' "^ 



The fossils and the rock-specimens were both obtained from the 

 same place, from those blocks which are on the beach below the 

 villas, blocks detached from the Bridport Sands, into which they 

 have been faulted. The latest finds (1919) — similar ammonites, a 

 Perisphinctid, and a JSfcnitihis — were all extracted from the bank 

 in the pathway below the villas. 



Why Mr. Richardson made the assumption that the fossils and 

 specimens came from the Bed Bed it is difficult to imagine, 

 especially as the cliff-section with the Bed Bed is from a quarter to 

 half a mile away ; and I had remarked that ^ 



' there is [in the cliff-section] practically no sign of any deposit of a thick 

 white bed of the character of the one that has just been described.' 



But the assumption was necessary to fit the percolation theory, in 

 pursuance of which Mr. Bichardson remarks that ' the lithographic 

 stone might be found associated wdth fossils of any hemera.' ^ The 

 difficult}^ here is that the fossils would show internally the different 

 matrices formed during the hemene to wdiich they right]}" belonged. 

 But these fossils from the white bed show inside and outside a 

 white-bed matrix — they are evidently synchronous wath the White 

 Bed. Another objection is that the fossils of the White Bed are 

 not found in any other of the Burton deposits. And there is a still 

 further objection which may be taken to the percolation theor}-^ — 

 that percolation w^ould not produce a fine-grained, laminated 

 lithographic stone. 



1 IX, 2, p. 56. 2 IX, 2, pp. 56-57, '^ I, 5, pp. 69-71. 



4 I, 5, p. 71. 5 IX, 2, p. 57. 



