ZONE OF AMMONITES OBTUSUS. 



73 



Sect io)i from Ih-oad Leil(/c to Conistone Ledge, near Charmouth. 



No. 



1. 

 2. 



9 



%* • 



4. 

 5. 



C. 

 7. 



10. 

 11. 

 12. 

 13. 

 14. 

 15. 

 IG. 

 17. 



LlTHOLOGY. 



Organic Remains. 



ft. in. 



Dark - gray limestone. " Cornatone 

 Ledge." 



Daik-l)Iuisli marls 20 



Dark-gniyisli limestone 10 



Dark clays. 



Dark limestone, witb septaria. 



Dark shale. 



Dark limestone, " Upper Cement- 

 bed." 



Dark sjiales, containing raudstone no- 

 dules at the base. 



Thill band of limestone. The " Penta- 

 crinite-bed." 



Dark sliales. \ 



Dark limestone. 



Dark shale. "Fire-ledge." 



Dark limestone. 



Dark shale. " Split-lcdge." 



Dark limestone 



Dark shales 



Grayish limestone 



Iclithyosaurus platijodon, Conyb., and I. inlermedius, 

 Conyb. Ammonites Birchii, Sow. 



Nautilus striatus, Sow., Ammonites Brooldi, Sow., 

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



Scelidosaurus Harrisonii, Owen. Inoceramus. 



Extracrinus Briareus, Mill. 



18. Dark marls, with nodular masses 20 



19. Dark indurated shale and limestone. 



" Broad Ledge." 4 



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



Saurian skeletons. 



Ammonites obtusus, Sow., and Am. Birchii, Sow., 



crystallised, forming the " Tortoise-ammonites." 

 The nodules of these lower Cement-beds contain 



Saurian remains. Pentaa-inus, n. sp. 

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



The zone of Anmonites obtusus 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 Ammonites 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 cliflF, which contains nodules with very large 

 specimens of Ammonites obtusus, Sow., Am. stellaris, Sow., and Am. Brooldi, Sow. 

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

 the form of the Ammonites. 



10 



