178 Jo/ms : The Permian Suit Lake. 



salinity was increasing,'' notwithstanding'. The succeeding marl 

 notes the appearance of more sediment-bearing water, and then 

 we have the thick bed of anhydrite, during which concentration 

 of the salt constituents of the lake must have reached the point 

 of saturation for sodium chloride. It should now be made clear 

 that in the case of sodium chloride, complete saturation means 

 that some of the salt must have been present in the solid form. 

 The purity of the anhydrite, and its freedom from interbedded 

 sediment indicates the extreme aridity of the climate just as 

 clearly as the extreme salinity of the water does. 



Another influx of muddy water left its sediment lying on the 

 anhydrite, and after the last layer of gypsum had been deposited 

 from the now less salt-laden water, a final layer of marl brought 

 the Permian period to a close. With it ended the Palaeozoic 

 era that had been born when the mighty Cambrian sea, with 

 its wonderful Trilobitic fauna, flowed over the pre-Cambrian 

 land surface — it expired in the miserable salt lake of the 

 Permians, now buried deep below the surface of the fertile 

 Vale of ^'ork. Yet before the wind-blown* sands of the 

 Triassic desert had hidden its last sediments, an obscure 

 chapter had been written on the saline pages of the upper 

 marls. It was written in characters hard to decipher, but 

 yielding at last their secret story to the patient worker who, in 

 his laboratory, spent ten years in the laborious task. All 

 honour to \'ant' Hoff and his brilliant helpers. 



Those who take the trouble may now learn how the humid 

 swamps and morasses of- the coal measures subsided under the 

 waters of the Permian Sea. How stage by stage that sea 

 contracted in volume, laid down the massive lower Magnesian 

 Limestone, and then after the middle marls came the thinly 

 bedded upper limestone in a much diminished sea. Then came 

 the final dwindling into the salt lake whose history we have 

 been discussing. 



This lake ivas saiu rated with eommon sail, and its tern pe rain re 

 for a considerable lime must have been 30^ C. , that is 86'^ F. 



It does not require much imagnnation to conjure up a picture 

 of that dwindling and shrunken salt lake, its sun-baked shores, 

 and the distant but lowly Pennines dried and parched, from 

 whose surface the western winds and occasional torrents were 

 to carry the sands of the Triassic desert, and usher in the 

 Mesozoic era. 



Walcol (Jibson, ' North Staffordsliirr Co.illicKls ' 11505, p. 139. 



Naturalist. 



