THE MICROSCOPE IN GEOLOGICAL INVESTIGATION. 



311 



clear by the laborious researches of Frof. Owen ;' and the following may 

 be given as examples of their value: A rock-formation extends over 

 many parts of Eussia, whose mineral characters might justify its being 

 likened either to the Old or to the New Red sandstone of this country, 

 and whose position relatively to other strata is such that there is great 

 difficulty in obtaining evidence from the usual sources as to its place in 

 the series. Hence the only hope of settling this question (which was one 

 of great practical importance, since, if the formation were new Red. 

 Coal might be expected to underlie it, whilst if old Red, no reasonable 

 hope of Coal could be entertained) lay in the determination of the Organic 

 remains which this stratum might yield; but unfortunately these were 

 few and fragmentary, consisting chiefly of teeth which are seldom per- 

 fectly preserved. From the gigantic size of these teeth, together with 

 their form, it was at first inferred that they belonged to Saurian Reptiles, 

 in which case the Sandstone would have been considered as New Red; 

 but Microscopic examination of 



their intimate structure unmis- FIG. 492. 



takably proved them to belong 

 to a genus of Fishes (Dendrodus) 

 which is exclusively Palaeozoic, 

 and thus decided that the forma- 

 tion must be Old Red. So 

 again, the Microscopic examina- 

 tion of certain fragments of 

 teeth found in a sandstance of 

 Warwickshire, disclosed a most 

 remarkable type of tooth-struc- 

 ture (shown in Fig. 492), which 

 was also ascertained to exist in 

 certain teeth that had been dis- 

 covered in the ' Keupersand- 

 stein ' of Wurtemberg; and the 

 identity or close resemblance of 

 the animals to which these 

 teeth belonged having been 

 thus established, it became 

 almost certain that the Warwickshire and Wurtemberg sandstones were 

 equivalent formations, a point of much Geological importance. The 

 next question arising out of this discovery, was the nature of the animal 

 (provisionally termed Labyrinthodon, a name expressive of the most pecu- 

 liar feature in its dental structure) to which these teeth belonged. They 

 had been referred, from external characters merely, to the order of Sau- 

 rian Reptiles; but it is now clear that they were gigantic Salamandroid 

 Amphibia, having many points of relationship to Ceratodus (the Austra- 

 lian 'mud-fish'), which shows a similar though simpler dental organiza- 

 tion. 



705. The researches of Prof. Quekett on the minute structure of bone* 

 have shown that from the average size and form of the lacunae, their dis- 

 position in regard to each other and to the Haversian canals, and the 



Section of Tooth of Labyrinthodon. 



1 See his magnificent " Odontography. " 



2 See his Memoir on the ' Comparative Structure of Bone,' in the " Transact, of 

 the Microsc. Soc.," Ser. 1, Vol." ii.; and the "Catalogue of the Histological 

 Museum of the Roy. Coll. of Surgeons," Vol. ii. 



