352 PRINCIPLES OF STRATIGRAPHY 



density of the water, they will soon die, and their remains become 

 embedded within the layer of silt. 



The Bitter Lakes of Sues an example. A characteristic exam- 

 ple of this type of deposit was formed in the Bitter Lakes on the 

 Isthmus of Suez, and which before 600 B. C. formed the Heroopo- 

 lite Gulf, a continuation of the present Gulf of Suez and the Red 

 Sea. After the gulf became separated by silting up to such an ex- 

 tent that the supply of water from the Red Sea just balanced the 

 evaporation from the surface of the gulf, and the salinity was of 

 corresponding magnitude, salt began to deposit, and continued until 

 some time after complete separation from the Gulf of Suez, and 

 transformation into the Bitter Lakes, when only the intensely saline 

 mother liquor remained. When in 1 861 -1863 the present canal 

 was cut through these lakes, a mass of salt 13 km. long, 6 km. broad 

 and averaging 8 m. in thickness, was found. In the center of Great 

 Bitter Lake, this salt mass was estimated at 20 meters in thickness. 

 The salt was of course quickly dissolved by the fresher waters of 

 the canal which pass through these lakes, but until 1869 the salt 

 beds were still covered by a layer of mother liquor. 



When discovered (Bader-4), the salt mass consisted of parallel 

 layers of varying thickness separated by thin layers of earthy mat- 

 ter and gypsum. Soundings to a depth of 2.46 m. showed 42 lay- 

 ers of similar composition and varying from 3 to 18 cm. in thick- 

 ness, while the earthy layers between them were only a few milli- 

 meters in thickness. At a depth of 1.47 m. from the surface were 

 found a bed of mixed powdery gypsum and clay 0.112 m. thick and 

 a bed of pure powdery gypsum 0.07 meter thick. The clay layers 

 were as a rule richly fossiliferous, containing the shells of numer- 

 ous genera and species of molluscs now living in the Red Sea. 



There is here illustrated a long succession of flooding and par- 

 tial drying up of these Bitter Lakes. On the influx of the waters 

 from the Red Sea, mud was deposited, followed quickly by deposi- 

 tion of gypsum. After this the salt crystallized out, with an admix- 

 ture of magnesium sulphate. As the waters became concentrated, 

 the animals perished and their shells sank to the bottom, where 

 they became embedded in the growing deposit. 



The amount of bittern salts in the mother liquor which covered 

 the salt beds of these lakes until 1869 was insufficient for the quan- 

 tity of salt found deposited in these lakes. It must therefore be 

 assumed that on the successive inundations from the Red Sea the 

 mother liquor then present was partly carried out in diluted form, 

 and that the quantity last found represented only the residue since 

 the last flooding of the lakes and the closing of the bar. The 



