Vol. 50.] ANNIVERSARY ADDRESS OF THE PRESIDENT. 73 



is well known, he observes, that in more recent limestones the 

 interstices of the constituent organisms are generally occupied by a 

 quantity of calcite. In this case the original calcite of the lime- 

 stone can easily be recognized by its large clear crystals ; whilst, 

 on the other hand, the altered portion of the limestone is repre- 

 sented by small crystals in aggregates, and these are usually stained 

 by iron oxides. So far, he says, as the evidence warrants a con- 

 clusion being drawn, the Devonian Limestones of South Devon 

 appear to have chiefly originated from corals, crinoids, ostracoda, 

 stromatoporoids, and fragments of shell ; some limestones even 

 representing coral-reefs, others coralline debris ; the Goniatite 

 Limestone alone contains foraminifera. There is little, perhaps, in 

 this which has not previously been indicated by macroscopic evi- 

 dence, but it is satisfactory to find that evidence confirmed by the 

 microscope. 



In discussing the more distinctly mineralogical questions, the 

 Author alludes to the occasional occurrence of rhombohedra of dolo- 

 mite. The micas, he thinks, may be of detrital origin, but this is 

 by no means certain. Minute crystals, referred to as ' microlithic 

 needles,' resemble ' clay-slate needles,' but are not always straight ; 

 they occur in every fine residue, and as inclusions in siliceous and 

 micaceous flakes. The siliceous fragments which enclose them 

 frequently contain many liquid inclusions. These points were well 

 illustrated, and the investigations generally were regarded as of great 

 value in illustrating the history of mineral growth and develop- 

 ment. Dr. Sorby, who was present at the discussion, referred to 

 the fact that he had himself been led to study the Devonian Lime- 

 stones of Devonshire chiefly on account of the valuable evidence 

 they afford in connexion with the cause of slaty cleavage. He 

 thought that, taken as a whole, no group of limestones presents a 

 greater range of character ; for not only must their original nature 

 have varied extremely, but the amount of change due to chemical 

 reactions and to pressure had, in many cases, been considerable. 



The South Devon rocks have, in addition to this paper by 

 Mr. Wethered, formed the subject of two extremely interesting 

 communications to the Society. In the first place, there was the 

 late Mr. Champernowne's notice of the Ashprington volcanic series 

 on the banks of the Dart below Totnes. This was a posthumous 

 paper, which we owe, in a great measure, to the care and solicitude 

 of Sir Archibald Geikie, and as he has dealt with the subject 

 fully in one of his Presidential Addresses, there is no need on the 



