30 TYPE AMMONITES— VI Oct. 



comparative length of primary and secondary ribs in specimens which 

 are crushed flat. 



Until these various faunal and stratigraphical statements can be 

 refuted, not by mere surmise, but by quite definite evidence, one must 

 decline to accept the conclusions of the Survey or of Dr. Neaverson that 

 the similar-looking biplex ammonoids of Chapmans Pool and Hartwell 

 are specifically identical or even sufficiently approximate to warrant 

 the statement that their respective deposits are isochronous. My visit 

 to the Dorset Coast this summer (1926) has shown that the claims of 

 Dr. Neaverson, as to how the upper part of Hartwell Clay is to be 

 correlated, and what the Dorset Portland Sands represent, are far too 

 hasty. The visit has enabled considerable advance to be made in the 

 correlation of the Upper Jurassic strata, as will now be detailed. 



Dorset Coast Strata : During a visit this summer to the Isle 



Fig, I. Hounstout Cliff and Chapmans Pool x 000027 O"" i : 359^ ; taken 

 from about S.S.E. A. Chapmans Pool ; B. Old road, foundered in places ; 

 C. Hounstout Cliff above road. For explanation of small letters see text. 

 Summary, p. 34, 



of Purbeck I had the good fortune to meet Mr. C. H. Waddington, 

 who had commenced a study of the Portland Sands of Hounstout Cliff, 

 Kingston. Mr. Waddington's assistance I most gratefully acknowledge : 

 owing to the short time at my disposal, and my limited capacity for 

 the fatigue of climbing, his help was extremely valuable. He showed 

 that the cliff of Hounstout was quite readily climbable, especially just 

 west of the shoulder seen to the left in Fig. i, and he was able to prove 

 positions in situ and confirm my surmises as to the beds from which 

 had come specimens collected from various fallen blocks. He is 

 continuing his researches, and there is every reason to suppose that 

 he will be able to make important additions to the more exact correlation 

 of Portlandian-Kimmeridgian strata of Dorset. 



