SUBDIVISION OF THE CHALK FORMATION. 



381 



plants, sponges, corals, echinoderms, belemnites, ammonites, 

 nautilites, fishes, reptiles, and other 

 marine exuviae, with occasional in- 

 stances of wood and plants drifted 

 from the land, the whole presenting 

 forms of life specifically distinct from 

 those occurring in the overlying beds ; 

 110 species discovered in the chalk being 

 identical with t?iose of the tertiary 

 deposits. They form the spoils of g 

 a primeval sea, which rivalled in g 

 extent the mighty oceans of the ^ 

 southern hemisphere at the present 

 day ; as the chalk group extends over 

 portions of the British islands, various f 

 parts of France, Germany, Denmark, |' 

 Sweden, Russia, and North America, g 1 



This ideal section (fig. 267) from 3 

 London to the Isle of Wight, shows g 

 the relative position of the tertiary g 

 cretaceous and wealden groups, with g- 

 the axis of elevation and subsidence {? 

 observed in the region through which g 2 

 the line of the section is supposed to | 

 pass. 



On the coast of Dorset, and in the 

 Isle of Wight, the chalk strata are ! 

 sometimes vertical; the line of dis- 

 turbance which upheaved the tertiary 

 beds of Whitecliff and Alum bays pro- 

 duced this position of the chalk rocks. 2, 



It was long ago observed by Sir H. 51 

 Englefield, that the flints in the ver- 1: 

 tical beds of chalk are all fractured 

 and fall to pieces when taken out of 

 their matrix ; proving the suddenness 

 of the convulsion which shattered them. 

 The beautiful section (fig. 268) of 

 Sallard Head shows the junction of 

 vertical and contorted chalk strata. 



ORIGIN OF THE CHALK AND FLINT. The idea which 



