Maiu — On Suhaenal and Marine Denudatmi. 451 



a line as possible, whether it be on the vertical cli£f face, tbe straight 

 lines of coast, or the level surfaces of sea coast reefs. As regards 

 vertical cliffs, the action of running water in river channels will 

 occasionally produce similar results to the sea, but in all other 

 respects the effect of subaerial denudation seems to be the production 

 of a sinuous outline and a rounded undulating surface. Now as the 

 straight element in the form of the ground is altogether subordinate 

 to its rounded contour, it seems impossible to resist the conclusion, 

 that rains and rivers have been the all powerful agents in modelling 

 the land ; indeed, the distinctive features of marine and subaerial 

 denudation seem almost unconsciously recognized when the advocates 

 of marine denudation point to the exceptional cases of terrace-struc- 

 ture in proof of the former action of the sea, and thus im wittingly 

 admit some other agency to accoimt for the almost universally rounded 

 form of the land surface, and the sinuous disposition of its lines of 

 equal height. 



Note. — It has been suggested to me that in the paper " On Watersheds," in the 

 Geological Magazine of August, I used the term Watershed in rather too general 

 a sense. I wish to explain that, in speaking of watershed areas, I merely referred to 

 the individual tracts defined by the lines of watershed. I may also have inadvertently 

 fallen into the use of the word as descriptive of an area, instead of a line, from the 

 idea that was before me of the watershed line structure, branching downwards from 

 the main line of watershed and ramifying over the whole area it includes, in the same 

 sense that the ramifications of the waterflow branch upwards over the whole area to 

 the watershed. 



rV. — Note on the Mimosa-Dale Chalybeate, Uitenhage, South 



Africa. 



By A. H. Chuech, M.A., F.C.S., E. A. College, Cirencester. 



ASIMALL quantity of a highly ferruginous water was lately given 

 to me for analysis by my friend and former colleague, Dr. John 

 Bayldon. He had collected the sample himself at the spring in 

 Mimosa-Dale, Uitenhage, South Africa, where also he had obtained 

 specimens of the iron-salts which are freely deposited by the chaly- 

 beate waters. 



The incrustation consisted of a crystalline ferrosoferric sulphate 

 containing a good deal of water. In chemical and physical characters 

 it approached Misy, but its occurrence as an abundant natural 

 deposit covering the ground about the spring for a considerable 

 vspace is of peculiar interest. Misy, it is well known, occurs in the 

 waters of the Eammelsberg mine, near Goslar, in the Hartz, but 

 neither in the abundance nor under the conditions of the Mimosa 

 Dale deposit. 



The water was found to contain 63.49 grains of solid matter per 

 imperial gallon. It had a strong acid reaction, and a most decided 

 styptic taste. By means of a direct iron determination, by the per- 

 manganate process, in the original water, together with an estima- 

 tion of the total iron present in the water after it had been treated 



