THE MICROSCOPE IN MINERALOGY AND GEOLOGY. 97 



ter of the organic nature of those serpentine limestones 

 in the Laurentian formations of Canada and elsewhere, 

 which are products of the growth of the gigantic forami- 

 niferal Eozoon Canadense, over immense areas f the 

 ancient sea-bottom, is one of still greater interest both to 

 the student of Geology and of Biology. 



This immense rhizopod appears to have grown one layer 

 over another, and to have formed reefs of limestone as do 

 the living coral-polyps. Parts of the original skeleton, 

 consisting of carbonate of lime, are still preserved, while 

 certain interspaces have been filled up with serpentine and 

 white augite. 



Microscopic Paleontology. As a general rule it is only 

 the hard parts of animal bodies that have been preserved 

 in a fossil state. 



It will often occur that the inspection of a microscopic- 

 fragment of such a fossil will reveal with certainty the- 

 entire nature of the organism to which it belonged. Thus 

 minute fossil corals, the spines of Echinodermata, the 

 eyes of Trilobites, etc., will determine the position to 

 which we should ascribe the specimen, or a section of tooth 

 or bone will enable the rnicroscopist to assign the fossil to 

 its proper class, order, or family. Thus Professor Owen 

 identified by its fossil tooth, the Labyrinthodon of War- 

 wickshire, England, with the remains in the Wittemberg 

 sandstones, and declared it to be a gigantic frog with some 

 resemblances both to a fish, and a crocodile. This predic- 

 tion the subsequent discovery of the skeleton confirmed. 



The minute structure of teeth differs greatly in differ- 

 ent animals. In the shark tribe of fishes the dentine is 

 very similar to bone, excepting that the lacunae of bone 

 are absent. In man and in the Garni vora the enamel is a 

 superficial layer of generally uniform thickness, while in 

 many of the Herbivora the enamel forms with the cemen- 

 tum a series of vertical plates which dip into the substance 

 of the dentine. Enamel is wanting in serpents, Edentata, 



