i'^Q Reports and Proceedings. 



was thought that this rounding of the crystals was caused by fusion, 

 but the lecturer remarked that it was often the most infusible of 

 minerals that had their angles rounded. These crystals of foreign 

 minerals belong to veins. A portion of a vein was exhibited con- 

 taining, first, a layer of apatite, then one of quartz, then a coating of 

 white calcspar, and lastly, a layer of sulphate of barytes. Another 

 showed a layer of orthoclase, then one of pyroxene, and lastl}^ one 

 of graphite. Some geologists have thought that these crystalline 

 limestones have an eruptive origin, analogous to trap ; but the beds, 

 the lecturer stated, are distinctly stratified. Crystalline limestones 

 are either indigenous, that is, are formed in situ, or they are endo- 

 genous, i.e., have been formed by crystallization in veins. A rounded 

 crystal of apatite, from a cavity, was exhibited. 



It was stated that springs containing mineral matter in solution 

 sometimes are affected by great chemical changes, and that, perhaps, 

 in this way the same waters which produce crystals, under altered 

 chemical conditions, have, in some cases, the power of wholly or 

 partly re-dissolving them, and rounding their angles. Crystals of 

 apatite and quartz, supposed to have been thus rounded, were ex- 

 hibited. The crystals of felspar were said to be indissoluble, and 

 as further examples, crystals of spinel, oriental ruby, brown tour- 

 maline and of pyroxene, from the crystalline limestones were shown, 

 presenting sharp and unrounded angles. 



In the indigenous rocks, also, that is in the main body of the 

 limestones, many of the foreign crystals are rounded, but not as in 

 the vein stones. 



Attention was then called to the discovery of organic life in these 

 ancient rocks, and a description was given of the Eozoon. It was 

 shown that the chambers of the shell of this species became filled 

 with serpentine or pyroxene, the crystals of which have thus ac- 

 quired a rounded form. It was stated, also, that Dr. Gumbel, who 

 has studied closely the Laurentian rocks of Bavaria, had determined 

 that many other rounded crystals of foreign origin in crystalline 

 limestones are due to organic agency. 



Principal Dawson moved a vote of thanks to the lecturer, and in 

 doing so took occasion to defend the genuineness of the discovery of 

 organic life in Laurentian rocks, and stated the doubts entertained 

 by some Irish naturalists, as to the organic nature of Eozoon, were 

 entirely due to a misconception on their part, and that what they 

 had taken for Eozoon was mineral matter. 



cos-iaESi^oisriDEisroiB. 



To the Editor of the Geological Magazine. 



Sib, — In the February number of your Magazine, Mr. D. Forbes, 



in an article entitled " On the alleged hydrothermal origin of certain 



granites and metamorphic rocks," has made two recently published 



papers of mine the subject of some remarks. " The appearance of 



