514 THE JOURNAL OF GEOLOGY. 



of the calcareous nature of all the rocks of Florida. In the 

 Everglades this water is exposed in broad shallow sheets to ac- 

 tive evaporation, agitation and variations of atmospheric temper- 

 ature and pressure. Concentration of the solution and escape 

 of carbonic acid, including some of that in the bicarbonate in 

 solution, follow, and the neutral carbonate is produced in 

 excess of the amount that can be retained in dissolved form. It 

 is therefore precipitated in two forms — first, from the mass of the 

 water as a flocculent mud ; second, from the lower layers of the 

 water in contact with limestone as crystals forming an integral 

 part of the solid rock. 



The alternation of dry and wet seasons is accompanied by 

 concentration and sluggish flow, alternating with dilution and 

 flood currents. Therefore there are seasons of more active pre- 

 cipitation interchanging with those of more vigorous transporta- 

 tion and, perhaps, partial re-solution. In these latter seasons the 

 calcareous mud is swept beyond the shallow basin where it 

 forms, and enters as a suspended sediment into the Gulf circula- 

 tion. What part, if any, is dissolved, what is deposited as mud 

 in the lagoons along the coast, and what is swept into the silt 

 banks of the Atlantic, is not known. 



Conditions which produced similar results are described by 

 Gilbert as having existed in Lake Bonneville. 1 Tufa was depos- 

 ited on the shores of the lake at various stages, but most abund- 

 antly at the Provo stage, during which the water lingered longest 

 at one level. The occurrences are thus described: 



"The distribution of tufa along each shore is independent of 



the subjacent terrane No deposit is found in sheltered 



bays, and on the open coast those points least protected from 

 the fury of the waves seem to have received the most gener- 

 ous coating. These characters indicate, first, that the material 

 did not have a local origin at the shore, but was derived from the 

 normal lake water ; second, that the surf afforded a determining 

 condition of deposition." 



1 Monographs of the U. S. G. S. Vol. I, p. 167-168. 



