50 



MESSES. W. B. ANDREWS AND A. J. JTJKES-BROWNE [Feb. 1 894, 



Pig. 1 shows the curious arrangement of the beds which overlie 

 the thin layer of grey, brown, and black clay near the base of the 

 Purbeck series. 



Pig. 1. — Beds seen in Wockley Quarry. 



a. Laminated Clay. 



b. Grey Marl. 



c. Hard Fissile Marl. 



d. Marly Limestone. 



e. Yellowish Sandy Marl. 



f. Yellow Ferruginous Stone. 



West of the spot where this sketch was taken, the yellow sandy 

 marl descends and cuts out the grey limestone and marls, but con- 

 tains patches of grey marl and pebbles of the grey limestone ; while 

 at the eastern end of the quarry the yellow sandy marl is absent, its 

 place being taken by a loose grey marl resting on an irregular sur- 

 face of hard, light-grey, flaggy limestone, the top of the marl being 

 hard and passing in places into a grey limestone ; these beds are 

 between 6 and 7 feet thick. 



It is evident that much contemporaneous erosion took place 

 during the formation of this part of the series, and the details of it 

 vary in every ten yards. It appears to correspond with the ' Broken 

 Beds ' of the Dorset Purbecks. The grey beds seem to have been 

 deposited first, and to have been subsequently exposed to the action 

 of a strong current which disturbed them and in places completely 

 destroyed them, embedding the broken remnants of them in the 

 yellow sandy marl which was deposited as the strength of the current 

 diminished. The surface being thus levelled up again, an even floor 

 was formed, upon which the material of the yellow ferruginous stone 

 was quietly accumulated. 



On comparing the Wockley section with that of Chilmark Quarry, 

 it will be seen that neither the thick oolitic freestone of the Chil- 

 mark Portlandian nor the tufaceous Lower Purbeck limestones 

 are present at Wockley. There is certainly nothing which can 

 possibl} 7 represent the freestone, and the Lower Purbeck of Wockley 

 is so different from that of Chilmark that no one particular bed 

 can be recognized at both localities. If, however, the grey clay 

 (with limestone-pebbles) of the Chilmark section be on the same 

 horizon as the confused grey marls of Wockley, there would seem 

 to be a thickness of about 30 feet at the former locality, which is 

 represented by only about 2 feet at the latter. 



