-in the South Englisli Chalk. 451 



All the marl seams which were noticed have been recorded in the 

 above section. There are in addition a few partings, all of which 

 suggest that they have opened along thin marl seams, the marl of 

 which has been washed away or bleached beyond recognition. But 

 even crediting all tliese partings as actual marl seams, the paucity of 

 marl seams is very striking when their abundance in the Sussex and 

 Isle of Wight sections is considered. 



I did not observe evidence of sliding alojig the parting which marks 

 the' base of the zone of Marsupites. In the upper part of the cliii 

 tlie parting appeared to correspond with the bedding and to be an 

 opening along a marl seam, in which case sliding, if it took place, 

 Mould leave no clear evidence. AVhen the parting left this marl 

 scam close to the foot of the cliff and curved across the flint seams it 

 did not seem to shift them, as must be the case if there had been 

 sliding along it. 



On the east side of the recess under Middle Bottom the cliff line 

 runs out to high- water mark and then turns again east and the beds 

 oscillate slightly without any effective dip for a considerable distance ; 

 a further 6 feet of chalk becomes thus measurable, making a measured 

 total of 67 feet of quadratus chalk. The westward dip Avhich then 

 sets in and increases rapidlj- gives a downward section which is 

 practically undisturbed down to the top beds of the zone of 0. pilula, 

 and these beds agree exactly in thickness with the corresponding 

 beds on the other side of the syncline. Beyond this point the 

 clialk becomes almost immediately too disturbed for reliable 

 measurement. 



I am strongly disposed to think that if there is any actual 

 dislocation in tliis neighbourhood corresponding to the Purbeck fault, 

 it is not a fault but is dissipated into one or more slides along the 

 highly inclined bedding phmes of the chalk between the zones of 

 A. quadratus and M. cor-anc/uinum, the precise plane or planes of 

 sliding being determined by tlie lines of weakness offered by marl 

 seams. There are several wide partings at beach level, and one or 

 two at any rate seemed to correspond with marl seams on the other 

 side of Middle Bottom. 



B. Arish Mell. 



This is a most disappointing locality, for it might fairly be hoped 

 tliat its two sides would between them give a complete section of the 

 zones of 0. pilula and A. quadratus, whereas they do not give 

 a complete recognizable section of either. The accompanying map 

 will aid identification of the various points referred to in the 

 description ; the outline given fur the base of the cliff is intended 

 to represent beach level under summer conditions. 



1. £ast side. — This is another case in which Dr. Howe does not 

 give any reliable clue for re-identifying the zonal boundaries he 

 adopted. The following section will serve the same purpose as the 

 Scratchells Bay section, of giving subsequent explorers the use of my 

 tinds. The crashed flint seam close to the top of the Viniacrinus 

 band is easily recognized, and most of the other points can be 

 individually identifled. 



