THE WEALD. 



589 



ig. 676 Echinus (Hemicidarus inter- 

 media, Chalk). 



The remains of enormous reptiles are numerous in the Wealden forma- 

 tions ; crocodiles, lizards, turtles of gigantic size have been discovered* 



and most curious fossils have been disinterred 



in the Hastings district. The " Greensands" 



are separated by what is termed gault, a stiff 



blue clay found in Norfolk, Essex, and Kent. 



The Lower Greensand includes the well-known 



Kentish rag, or limestone, of which so many 



churches are built. The Upper Greensand is 



supposed to be a seashore deposit on the sides 



of an extensive ocean or sea, at the bottom 



of which the chalk was formed. After the 



Wealden beds were formed, they were covered 



by these greensand estuary-beds, or littoral 



strata. In these series new forms of life ap- 

 peared, and the waters became the receptacle of myriads of mollusca,etc., which 



in time formed the great chalk cliffs and downs so often referred to. The 



chalk is interstratified with sand, which as "gault" and " greensand" was 



probably the sand of the ocean bed before the 

 chalk was formed upon it, and the seas must have 

 supported many marine reptiles, for stony "nodules/* 

 or coprolites, which are the fossil excreta of the 

 animals, are found, and now used for manure, after 

 being buried for thousands of years. Examination 

 of these remains has resulted in the discovery of the 

 teeth and bones of fish which had been devoured by* 



the gigantic reptiles. An illustration of a shell thus discovered is annexed. 

 We have in a former chapter spoken 



of the chalk and its formation. We 



know that it is composed of the minute 



foraminifera. The fossil remains are very 



numerous in chalk and all of a marine 



kind, such as the ammonites, belemnites, 



and such cephalopods, and the echinus, 



bivalve mollusca, Crustacea, etc. We 



have occasionally flints appearing in the 



chalk, and this circumstance has given 



rise to some speculation as to how the 



flints got there, for they consist of nearly 



pure silica ; and the theory of the 



petrifaction of sponges, madrepores, etc., has been started to account for their 



presence. Dr. Carpenter says : " It may be stated, as a fact beyond all 



question, that nodular flint and other analogous concretions (such as agates) 



may generally be considered as fossilised sponges or alcyonian zoophytes, 



since not only are their external forms and their superficial markings often 



Fig. 677. Nautilus Inequalis. 



Fig. 678. Ammonite from the chalk. 



