THE HAMILTON ASSOCIATION. 7 I 



by Sir Win. Dawson, in chapter i, pages 14 and 15, of a recent 

 work, " The Chain of Life," on mineralization by the process of 

 infiltration. The conditions assumed by a Clinton " Farosites " 

 here, is precisely that of the tabulated coral represented in figure 2, 

 when the wall is silicified and the cells filled with silica. It seems 

 more difficult to understand why the spiral coils of some of " the 

 Silurian" and "Carboniferous" Brachiopods, "Spirifera," " Atrypa," 

 etc., are so beautifully displayed in a silicified condition, while the 

 remainder of the interior of the shell is often perfectly hollow. 



The Director-General of The Ohio State Survey (Dr. 

 Newberry) mentions a very remarkable instance where a modern 

 plant (or lichen) had stamped its impression on a quartz (silex) 

 pebble by dissolving the flinty material with which it came in contact. 

 The following paragraph occurs, page in., vol. XL, "Proceedings of 

 The Ohio Survey :" "Some years since, at a meeting of The American 

 Association, the Geologists present were much puzzled by some 

 specimens of the Conglomerate (carboniferous) exhibited by Prof. 

 Brainerd, of Cleveland, in which the impressions of the stems of 

 plants were as distinctly transmitted to the quartz pebbles as to the 

 interspaces of sand." 



Prof. Brainerd argued from these specimens that the pebbles 

 were of concretionary origin, and that they bore the marking of 

 the bark of plants because they had been formed in contact with 

 such bark. The recent experiments of Thenard which show that 

 numic acid renders silica readily soluble, afford an easy solution of 

 the problem, and confirm the view taken by the writer upon the 

 occasion referred to above, viz ; " that the pebbles had been dis- 

 solved away where in contact with the plant." Here we have 

 apparently a well authenticated instance of a modern plant possessing 

 an acid sufficiently strong in its natural state to corrode and eat its 

 way into " the quartz." Professor Sollas, now of Trinity College, 

 Dublin, some years ago, pointed out how the silica of sponges was 

 rendered easily soluble and often replaced by "calcite." Un- 

 fortunately, I cannot find the paper, which has been mislaid or lost. 

 I am quite satisfied that such is the case. The impure limestones 

 of "The Burton Niagaras" which overlie "the chert band,*' frequently 

 display a mere outline of the form of a sponge, which had disappeared 

 and been replaced by a softer mineral. 



