ZONE OF AMMONITES OBTUSUS. 



73 



Sedion from Broad Led(je to Cornstone Ledge, near Charmouth. 



LlTHOLOGY. 



Organic Remains. 



No. 

 1. 



ft. in. 



4. 

 5. 



6. 

 7. 



10. 

 11. 

 12. 

 13. 

 14. 

 15. 

 16. 

 17. 



Dark -gray limestone. "Cornstone 

 Ledge." 



Dark-bluish marls 20 0 



Dark-grayisli limestone 0 10 



Dark clays. 



Dark limestone, with septaria. 

 Dark sliale. 



Dark limestone, " Upper Cement- 

 bed." 



Dark sliales, containing mudstone no- 

 dules at tlie base. 



Thin band of limestone. Tlie " Penta- 

 crinite-hed." 



Dark sliales. 



) "Fire-ledge." 



Dark limestone. 

 Dark shale. 

 Dark limestone. 

 Dark shale. " Split-ledge." 



Dark limestone 



Dark shales 



Grayish limestone 



18. Dark marls, with nodular masses 20 0 



19. Dark indurated shale and limestone. 



" Broad Ledge." 4 0 



Ichthyosaurus pi atyodon, Conyb,, and/, intermedius, 

 Conyb. Ammonites Birchii, Sow. 



Nautilus striatus. Sow., Ammonites BrooJdi, Sow., 

 and Am. stellaris, Sow. (very large). 



Scelidosaurus Harrisonii, Owen. Inoceramus. 

 Extracrinus Briareus, Mill. 



Ammonites planicosta, Sow., and Am. Smithii, Sow. 

 Saurian skeletons. 



Amtnonifes ohtusus. Sow., and Am. Birchii, Sow., 

 crystallised, forming the "Tortoise-ammonites." 



The nodules of these lower Cement-beds contain 

 Saurian remains, Pentacrinus, n. sp. 



This bed overlies the Lima-series east of Lyme-Regis. 



The zone of Ammonites ohtusus probably attains a thickness of from 80 to 100 feet; 

 its actual measurement would be a matter of difficulty, from the manner in which the 

 marls have covered over the bands of limestone ; hence the imperfection of our estimate. 



In the lower slaty marls are numerous compressed Ammonites Birchii, which fall to 

 pieces when removed from the matrix. Higher up (No. 17) the same species is found in 

 fine preservation, with Ammotiites obtusus. Here the shells are replaced, and the septa 

 filled, with crystallised carbonate of lime. These beautiful specimens are the " Tortoise- 

 ammonites " of local collectors. About 40 or 50 feet above the latter an irregular band of 

 limestone (5) is seen projecting from the cliff, which contains nodules with very large 

 specimens of Ammonites otjtasus. Sow., Am. stellaris. Sow., and Am. Brookii, Sow. 

 Most of the nodules have a septarian structure, the veins of spar intersecting and distorting 

 the form of the Ammonites. 



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