244 A. F. Foerste — Chipola Miocene of 



not appear however, that any iodine was set free, none could 

 be extracted with alcohol. 



Mercuric oxy chloride, 2HgO, HgCl 2 ; heavy pressure caused 

 much darkening. 



Sodium thiosulphate with a moderate pressure compresses 

 to a hard translucent cake but does not undergo any decompo- 

 sition. 



To the foregoing cases are to be added those of the three 

 silver haloids described in a previous paper : these blackened 

 with a quite moderate pressure even in the case of the iodide. 



Although in all these instances the darkening is well 

 marked, still the actual proportion of material affected is small, 

 so that in many cases it is difficult to apply tests to decide as 

 to the precise nature of the substances formed. In some cases, 

 however, this can be done and we are justified in concluding 

 that many of the salts of easily reduceable metals, especially of 

 silver, mercury and platinum, undergo reduction by pressure. 

 Such reactions are endothermic and it therefore follows that 

 mechanical force can bring about reactions which require ex- 

 penditure of energy, which energy is supplied by mechanical 

 force precisely in the same way that light, heat and electricity 

 supply energy in the endothermic changes which they bring 

 aboiit. 



In the second part of this paper additional support will be 

 adduced for these conclusions. 



August, 1893. 



Art. XXX VII. — Studies on the Chipola Miocene of Bain- 

 bridge, Georgia, and of Alum Bluff, Florida, with an at- 

 tempt at correlation of certain Grand Gulf group beds with 

 marine Miocene beds eastward ; by Aug. F. Foerste. 



The Miocene strata of Georgia, Florida and Alabama can be 

 divided quite conveniently into three groups. Beginning with 

 the older, these would be called in northwestern Florida, the 

 Chattahoochee, Chipola, and Chesapeake Groups. The Chat- 

 tahoochee contains an assemblage of fossils decidedly Miocene. 

 A considerable number of forms have close affinities with 

 those of Chipola age, while a decidedly less close relationship 

 is found to exist with forms from the Yicksburg Eocene, at 

 least as far as could be determined by comparison with those 

 Vicksburg fossils actually discovered by us in southwestern 

 Georgia. The facies of the Chipola fauna is decidedly 

 southern, sub-tropical in fact, and there are many species iden- 





