514 PBOCEEDINQS OF THE GEOLOGICAL SOCIETY. 



Crassatella complicata, and Trigonia Goldfussi make their appearance. 

 These rocks, it will be remembered, I have looked upon as the upper- 

 most of the Zwartkops- and Simdays- River strata. At the Government 

 Saltpan, Trigonice. and Turritellce are mixed with the remains of Cida- 

 ris — while in the section near the Salt Vlei (Sect. S, fig. 6, 3) we find 

 Crassatella complicata and T. Goldfussi, together with a Oervillia 

 (shells fonnd in the uppermost Sundays-Eiver strata), imbedded in 

 a sandstone, immediately above which are found stratified clays con- 

 taining shells which, together with Crassatella complicata, are asso- 

 ciated with Cidaris pustulifera, the characteristic shell of the fossi- 

 liferous zones of the SaHferous Strata, and, apparently, i:he Trigonice, 

 Ammonites, and their associates are absent. This explanation proves, 

 I think, the regular sequence of the shells. 



Mr. Tate, in his paper " On some Secondary Fossils from South 

 Africa," says*: — " Species of this type (^Cidaris pustulifera) exist 

 at the present time, and are found in the Tertiary and Creta- 

 ceous rocks ; species of the type with crenulated bosses characterize 

 Oolitic deposits. There are, however, some exceptions to these rules, 

 and for the present the African species may be regarded as another 

 exceptional example." If I understand this rightly, some species 

 of Cidaris (this fossil, remember, is associated with Crassatella 

 complicata') are indicative of Cretaceous rocks ; but this is an " ex- 

 ceptional case." If, then, these same deposits are placed in the 

 position which I believe is their true one, the exceptional condition 

 vanishes ; they take their right place, and prove that the law which 

 regulated, with regard to periods, the development of particular 

 races was the same in the southern as in the northern hemisphere. 



Origin of the Salt. — The author thinks that the Trigonia-series, hav- 

 ing been deposited in open sea, would be less likely to contain salt than 

 shallow-water beds succeeding them and formed in narrowing creeks 

 and lagoons. The saliferous series he believes to have thus suc- 

 ceeded the Trigonia-heds, and to have become impregnated with 

 salt. At the present time the same causes are at work on a smaller 

 scale, in the mouths of some of the minor rivers of South Africa, where 

 the entrances are blocked up with sand and thus communication with 

 the ocean is cut oS, except when broken through occasionally by a 

 freshet after heavy rains. During the time that these mouths are thus 

 land-locked the evaporation is more rapid than the supply ; and as a 

 natural consequence, the water in the enclosed basins becomes more 

 intensely salt than that of the neighbouring sea. The deposits formed 

 within them are saturated with this extra-saline fluid, so that when 

 a flood bursts through the opposing barrier, and the water of the 

 imprisoned river faUs with the tide, banks of brackish mud are ex- 

 posed in many places ; and these soon prove themselves to be salife- 

 rous deposits ; for, as they dry in the sun, they become covered with 

 a white saKne efflorescence. Such, one cannot help believing, is 

 the explanation of the mode of formation, although on a grander 

 scale, of the saliferous strata we have been considering. 



* Quart. Joura. Geol. Soc. vol. xxiii. p. 163. 



