44 



ftlone deserve that name) are chiefly composed of vitri- 

 fiable matter ; and if they are sometimes found to eon- 

 tain sea-shells, it is never to great depths, though such 

 bodies are found in the adjacent vallies. 



Potters earth is found plentifully in most low grounds 

 and vailies, between mountainous tracts. By exposing 

 common flint stones to the confined vapour of boiling 

 water, a clay of the very same kind may be formed, and 

 is no more than a de-composition of flints. Hence it 

 appears that wherever this clay is to be found, there the 

 earth has undergone some violence by fire ; and that 

 this has been effected by earthquakes, soon after the 

 deluge, seems extremely probable. The deluge has 

 given origin to many fossil substances, and combinations, 

 which otherwise would not have happened. Chalk is. 

 no more than the ruins of sea-shells, and lime-stones 

 consist of the same bodies cemented together by a stony 

 juice. 



13. At fixed times the water of the sea runs for near 

 six hours from south to north, which is callecl the flood, 

 at which time it rises gradually on our shores, and in the 

 channels of the rivers. Then after standing at the same 

 height for a quarter of an hour, it returns for near six 

 hours from north to south, which we term the ebb ; and 

 after a quarter of an hour the water rises again. The 

 change thereof is twice in twenty-four hours, but begins 

 near fifty minutes later daily, And this is observed on 

 all the shores of Europe, that are washed by the ocean : 

 whereas the Baltic and Mediterranean sea, as well as the 

 Caspian, have no tides. The nearer we approach the 

 pole, the more impetuous the tides are. The cause of 

 them was wholly concealed from the ancients ; but it is 

 HOW well known to every one. They depend entirely 

 on the motion of the moon, with which they exactly 

 correspond : the flood beginning to rise just at the time 

 when the moon is in the meridian. 



There is something remarkable in the manner wherein 

 the tides rise, in several of our rivers. , In the river Se- 



