250 Mr. Webster on the Strata lying over the Chalk, 



*' with marine bodies. The thickness of the beds of stone varies 

 " from 6 to 12 feet. They contain river shells, bones, sculls of ani- 

 " mals, kernels of fruits, ears of corn, 6cc. These strata extend 

 " quite under the city to the borders of the Unstrutt, near to which 

 " are seen strata of alabaster and limestone, the detritus of which 

 " has probably given origin to these beds. It is to be remarked 

 " that no remains of marine animals are found above the clay where 

 " the ancient beds commence." 



A very interesting account has been given by Von Buch of a 

 freshwater formation in Locle in the district of Jura. It is con- 

 tained in ^ high inclosed valley surrounded by mountains of white 

 compact limestone ; and consists of various alternating beds of 

 marly limestone whitish and somewhat friable, bituminous shale, 

 eoal, hornstone of a smoke grey colour, and of a fine splintery or 

 imperfectly conchoidal fracture, and containing crystals of quartz ; 

 also of opal of a brownish black colour, glistening lustre, and perfect 

 conchoidal fracture. Both the limestone and hornstone contain fresh- 

 water shells, among which may be distinguished the helix cornea 

 and bivalves. 



From these and other accounts It appears probable that these 

 freshwater formations were purely local, and there appears no 

 necessity for supposing that the others were any thing more than 

 local deposits in a former state of the earth. 



I am aware that such formations have lately been traced on the 

 shores of the Baltic, in the south of France, Spain, Germany, and 

 Silesia ; but this can only prove that fresh water lakes were in for- 

 mer times as at present very numerous and often extensive. 



One of the most striking differences between these ancient lakes 

 and modern ones, as has been remarked by Messrs. Cuvier and 

 Brongniart, Is the property possessed by the former of forming 

 siliceous strata. 



