The Chalk strata in the Isle of Wight are of great thickness. In the Culver Cliff there are some 400 feet of flintless Chalk (Lower and Middle Chalk), and then some 1,000 feet of chalk with flints. There is some variation in the thickness of the strata in different parts of the Island, and the amount of the Upper strata, which has been removed by denudation, varies considerably. The average thickness of the white chalk in the Island is about 1,350 feet.[9] Including the Lower Chalk, the maximum thickness of the Chalk strata is 1,630 ft. The divisions of the chalk we have so far considered depend on the character of the rock: we must say a word about another way of dividing the strata. It is found that in the chalk, as in other strata, fossils change with every few feet of deposit. We may make a zoological division of the chalk by seeing how the fossils are distributed. The Chalk was first studied from this point of view by the great French geologist, M. Barrois, who divided it into zones, according to the nature of the animal life, the zones being called by the name of some fossil specially characteristic of a particular zone. More recently Dr. A. W. Rowe has made a very careful study of the zones of the White Chalk, and is now our chief authority on the subject. The strata have been grouped into zones as follows:-- Zones. Sub-Zones. { Belemnitella mucronata. { Actinocamax quadratus. { { Offaster pilula. Upper { Offaster pilula. { Echinocorys depressus. Chalk. { { Marsupites { Marsupites. { testudinarius. { Uintacrinus. { Micraster cor-anguinum. { Micraster cor-testudinarium. { Holaster planus. Middle { Terebratulina lata. Chalk. { Inoceramus labiatus. { Holaster subglobosus. { Actinocamax Lower { { plenus (at top). Chalk. { Schloenbachia varians.{ Stauronema { { carteri (at base). The method of study according to zoological zones is of great interest. The period of the White Chalk was of long duration, and the physical conditions remained very uniform. So that by studying the succession of life during this period we may learn much about the gradual change of life on the earth, and the evolution of living things.