228 PICTURESQUE SKETCHES 



sand." This bed is of moderate thickness in Eng- 

 land, but of far greater importance in this respect in 

 some parts of the Continent, where it is manifestly 

 the representative of an extensive and long- continued 

 series of operations. During this period the prevail- 

 ing material deposited was, in England, sand, varied 

 occasionally by calcareous and muddy bands, but on 

 the Continent it includes many beds of limestone. 

 The sands contain a good number of fossils very dis- 

 tinct from those of the oolitic period, so that the de- 

 posit of the Wealden beds had either occupied so long 

 a time that the species in the neighbouring seas had 

 died out and been succeeded by others, or else the 

 commencement of the deposition of these beds had 

 been marked by the introduction of a new series of 

 typical forms. 



The deposit of lower greensand was probably 

 made in a sea which in the south of England was 

 either shallow, or at least not extremely deep ; and 

 the bed of clay called gault, which rests upon the 

 lower greensand, contains forms for the most part 

 quite distinct from it. The group of deposits called 

 on the Continent " Neocomiari* is nothing more than 

 the typical form of these older or lower sandy beds, 

 either immediately succeeding the Weald or resting 

 directly on the oolite, though not deposited on the 

 latter beds till after a long interval had elapsed, 

 during which, probably, the oolitic rocks had formed 

 dry land* 



The gault, or blue clay reposing on the lower 

 greensand, is itself succeeded by another thin and 

 less important bed of sand, also containing pale green 

 particles, and for that reason called " upper green- 



