50 



TYPE AMMONITES— VI i""^ 



§ I — Troll Quarry, Thornford, Dorset 

 (Fullers' Earth Rock = Great Oolite, pars, 

 Thornford Beds, Tuhtan Age) 



Thickness 



Strata Eeet Ins. 



1. Top stone and marl : stone pale straw colour, somewhat 



hard. (This bed visible only about the middle 



of the west face of the quarry). [Tulophorites] i 8 



2. Pholadomya Bed : impersistent stone bed mixed with 



marl : stone rather hard, whitish, with occasional 

 pinkish tinge, especially when bruised by the 

 hammer. Large Pholadomyce ; Belemnites occa- 

 sionally in base. [Madarites] i o 



3. Marl and stone, mostly marl i ° 



4. Fairly persistent stone-band 4 



5. Rhynchonella Bed: Stone-band, hard, light straw 



coloured, shelly ; many Rhynchonellas and broken 

 shell-fragments. [Rugiferites] 3 



6. Marl and stone, mostly marl i 3 



7. Prominent band of blue-hearted stone, light brown 



outside. [Pleurophorites] • • 10 



8. Marly stone 4 



9. Hardish, blue-hearted stone, brownish outside [Pleuro- 



phorites] 5 • 



(Beds 7-9 form one prominent blue-hearted 



band at north-west corner of the quarry : it is 



about I foot 3 inches in thickness) 



At north-west corner of quarry, small 



temporary excavation : — 



10. Marl 5 



11. Hard bluish, somewhat argillaceous stone, perhaps the 



bed for Sphceromorphites 7 



12. Marl. 



Samples of the matrices of various stone-bands were brought away 

 and were compared with the matrices of the figured specimens. The 

 result was to give the following possible sequence : 



Tulophorites 



Madarites 



Rugiferites 



Pleurophorites 



Sphaeromorphites 

 which differs from the sequence given in Vol. iii, Table iii, p. 51. only 

 in the transposition of the two upper terms of the Thornford Beds. 

 But, of course, the sequence now given is based on no more than these 

 comparisons of matrices ; and, as the matrices do not differ sharply and 

 distinctly as in so many other cases— for instance, beds of Inferior 

 Oolite— but are unlike only in minor details, these comparisons may be 

 faulty. Short of being able to be present when the quarry is in work, 

 and then being prepared for days of attendance with very little result, 

 not much more can be done. The beds are very poorly fossihferous 

 so far as ammonoids are concerned ; there was not a single ammonoid 

 to be seen in all the long quarry face, and there were only a few fragments 

 lying about. The dozen or so specimens which I had got together were 



