319] G. E. Dorsey 



Zone 3 Some limestone, with Echinoconus conicus, Ananchytes 

 ovatus, Scaphites constrictus, Baculites incurvatus. 



Zone 4 Some marly sands, with Ananchytes sulcatus, Terelra- 

 tula fallax, and faxoensis, Pycnodonta vesicularis. 



The above is a good example of what is contairmally being 

 repeated in the recorded occurrences of this Belemnitella 

 form. Where there is a chalky or a glauconitic facies the 

 form is present. When this changes to anything else, it is 

 almost invariably absent. 



The most prominent exception to this, as will be seen from 

 the facies given above, is the area across the Alps, the basin 

 connecting the two main basins from England to Kussia and 

 from Sweden to France. Here B. mucronata occurs most 

 often in a marly or marly limestone facies. It is likely that 

 most of the surrounding country in the late Senonian was 

 peneplained, which would permit clear water in very near 

 shore deposits, and explain the occurrence of limestone with 

 marls. If B. mucronata, ranging far and wide over areas in 

 which chalk was being deposited were to stray into this basin, 

 open to the two regions of congenial habitat, they might either 

 pass through to the far basin, or die on the way. If such a 

 condition had existed we should expect to find the form 

 exactly as we do find it, erratically distributed in changing 

 lithology. 



If we pursue our search for B. mucronata farther to the 

 east, into Persia, Turkestan, Siberia, China, Japan, Alaska, 

 we everywhere find it absent. Although the Senonian is 

 present in much of this area, there are no occurrences of B. 

 mucronata recorded. 



The Senonian, as it occurs around the western shores of the 

 Mediterranean Sea, will afford a rather impressive illustration 

 of the way in which, with a change in the facies of the beds, B. 

 mucronata vanishes. In Sicily, and in Spain, the Senonian 

 is present as sands with occasional limy lenses. In Italy the 

 Hippurites limestone is well developed. In Tunis the late 

 Cretceous is represented by white limestones, alternating with 

 yellow marls. In the south of Tunis there is also a very well 



