164 THE MICROSCOPE 



species, and probably as little change has taken place in the dermo- 

 skeletons of the insects mummified in fossil resin, considering the 

 almost perfect condition of insects found in Amber. 



The microscope gives a fresh value to a fragment of tooth or 

 shell, too imperfect to be determined without a section, which will 

 frequently show minute, but characteristic structure ; and yet such 

 a fragment may serve to identify the nature of the formation in 

 which it was found ; a matter not only of importance to the 

 Palaeontologist, but also to those in search of minerals or water, 

 for the small core which the boring-machine brings up must often 

 of necessity contain but scanty evidence of the nature of the 

 strata through which it has drilled, and yet, on an accurate know- 

 ledge of these strata, success in many cases depends. 



Time and the use of the microscope must decide as to the 

 probability of organic remains being ever discovered in the 

 archaean Limestones, or of organic structure being traced in 

 Laurentian Graphite. The well-known Eozoon was thought for 

 awhile by some to have settled the question in part, but its mineral 

 nature and origin is now generally admitted. 



With regard to the Eozoon, in any case, the storm of con- 

 troversy which raged around it should prove useful as a warning. 

 How difficult even skilled observers find it at times to distinguish 

 in mixed and infiltrated minerals, what is due to strictly mineral 

 changes alone, and what to their modification, by the presence of 

 organic remains. Many fossils, even when their internal structure 

 seems best preserved, are only, either a complicated series of minute 

 casts, as many fossil sponges, or exist simply as stains in the silica, 

 which has, atom by atom, replaced those which once composed the 

 organism, leaving only some of the molecules of carbon, iron, or 

 lime with which it has entered into combination, without dis- 

 arrangement of their original distribution, so that they thus 

 remain to map out, in a sort of solid photograph, in permanent 

 type, many most beautiful and minute details of structure. These 

 ghosts of former structure remain, though not so easily traced, 

 even when the silica itself has in the course of time undergone a 

 molecular change, having passed from the colloid to the crystalline 

 state, for crystals are formed without regard to the presence or 

 absence of organic impurities in the matrix, and the pattern of the 

 structural remains becomes obscured by them. 



