On Dr. Rowers Zones of the White Chalk. 175 



There is evidence of erosion along the whole coast as seen in the 

 chalky heels with glauconitic grains, in which is a mingled fauna from 

 Cenomanian deposits and the lower bed of the White Chalk. At 

 Martin Rock the disappearance of the cuvieri-zone, etc., on the cliff 

 face affords an example of contemporaneous erosion, the beds having 

 been apparently deposited against a Greensand bank. The Terebratulina- 

 sea must have extended further westwards than the previous seas, and 

 that of Marsufites still further, for it has left its traces among the 

 flints of the Haldon Hills. 



Along this western margin of the Cretaceous sea, in its more littoral 

 conditions; we meet with the lowest occurrences of several White 

 Chalk fossils. Among the most interesting are the Micrasters, as 

 M. cor-hovis and M. leslcei both occur in the ctivieri-zone of Devon, 

 that is, lower in the series than in any other exposure in England. 

 If. cor-testudinariimi appears to have originated in eastern waters, 

 as this group-form is almost entirely absent in the planus- and cor- 

 testitdmarium- zones of the west. 



Yorkshire. 



The coast of Yorkshire is severe. It is distinguished from all other 

 English sections by the nature of the rock, the peculiar lithology 

 of the beds, the paucity and condition of the fossils, and its physical 

 conformation. There is no counterpart in the south to the grand 

 screes of Speeton, nor are the southern cliffs, however lofty, comparable 

 to the mighty tide-bound ramparts of Bempton. 



None but verj^ keen observers would have been able to define 

 around Elamborough Head the limits of the zones, and to fix their 

 boundaries within one or two feet, and the keenness of the authors is 

 clearly shown by the fixing of the zone of If. cor-testuclinarium below 

 Breil Head, where no man is known to have landed, and where the 

 rocks are so numerous that, even with the smallest sea on, their boat 

 would have been staved in. 



l^owhere do we see the workings of local variation in geographical 

 distribution of fossils more strongly brought out than in this county, 

 and yet we are still able to trace the continuity of life-forms, though in 

 a markedly attenuated degree. The zones of Rhynchonella ciivieri and 

 Terehratuli7ia are quite in a line with those of southern sections, poor 

 though the fauna is, and it is only when we reach the horizon where 

 Micraster usually helps us that the difiiculty begins. If. leskei, 

 If. cor-hovis, If. cor-testudinariuin were not found, but such Micrasters 

 or fragments of Micraster as were found agreed in all essential features 

 of the test with those in the zones of the more prolific south. The 

 same is seen in the zone of A. quadratus, for while the name-fossil is 

 absent, possibly by reason of the thinness of the beds, Cardiaster 

 2nllula, though notably rare, is found, as usual, at this horizon. The 

 zone of Marsupites, though lacking many of its characteristic guide- 

 fossils, exhibits the customary division into Marsupites- and Uintacrimis- 

 bands. 



Further, the vertical range of certain fossils, usually restricted in 

 their distribution, is so vast that their very persistence is bewildering. 

 As instances we quote a range of 800 feet for Act. granulatus, and 



