302 Mr Connell on the Chemical Nature of Fossil Scales^ 



tution will gradually decay, and if water holding calcareous or 

 siliceous matter in solution, has access to them, the place of the 

 perishing animal matter will probably be taken, to a greater or 

 less extent, by the dissolved mineral matter. The fossil scale 

 will thus consist, when the process of mineralization has been 

 completed, of the original animal earths, and of the substituted 

 mineral matter. On the other hand, if a saurian animal were 

 mineralized, the perishable animal matter, of the nature of coa- 

 gulated albumen, forming nearly the wjiole mass of its scales, at 

 least of such as are flat, and belong to the sides and belly, 

 would gradually be dissipated ; and if no mineral matter had 

 been presented to them during this process of decay, in such a 

 state as to be fit for substitution, no vestige of the scale will be 

 left ; but if such mineral matter has been present, it will pro- 

 bably gradually take the place of the decaying animal matter, 

 and we shall have a substance preserved, possessing the form 

 and even structure of the original scale, but containing little or 

 no bone-earth, because none existed in the original object, and 

 consisting entirely, or nearly so, of the replacing substance, 

 whether siliceous or calcareous, — just as we find perisiiable ve- 

 getable objects preserved in a mineral form in all the delicacy of 

 their original structure, although no longer presenting even a 

 trace of combustible matter. Assuming, therefore, the scales 

 of extinct saurians to have bad the same composition as those 

 of living reptiles, we shall expect to find true saurian scales, 

 where such exist, to contain little or no bone-earth, and to con- 

 sist almost entirely of the mineralizing substance. 



These principles would, I believe, have been sufficient to de- 

 cide the disputed question as to the nature of the organic re- 

 mains found in the limestone of Burdiehouse, had not that point 

 been previously settled on other grounds. The analysis of the 

 scales of that deposit has been already published in the Trans- 

 actions of the Royal Society of Edinburgh. Not only was it 

 found that they contained a large proportion of bone-earth, but 

 it was also ascertained that the proportions of the constituents 

 bore a very strong analogy to those of the scales of a recent fish, 

 supposed by M. Agassiz to be the living type of the Megalich- 

 thys of Burdiehouse. The siliceous matter in the fossil scales 

 had apparently taken the place of the perishable animal matter 



