Devonian Rocks. 91 



tive, as shewing the great importance of an examination of 

 the internal structure of the substance of fossil teeth by the 

 microscope, in determining the classes of animals to which 

 they have belonged. He points out, by a striking illustra- 

 tion, how the microscopic labours of the philosopher, in his 

 closet, may have the most important effect on questions 

 that appear to be far remote from the subject of his inquiry. 

 Had the teeth, under consideration, continued to be held to 

 belong to Saurians, the matrix in which they are imbedded 

 having a close resemblance in mineral character to magne- 

 sian limestone, or to members of the new red sandstone 

 series, borings for coal might have been carried on in many 

 parts of Russia, involving vast losses ; but the teeth having 

 been proved to belong to a class of fishes that are character- 

 istic of the old red sandstone, all expectations of finding pro- 

 fitable seams of coal are known to be vain. 



If we now cross the Atlantic with Mr Lyell, and visit the 

 Silurian region of North America, we find that series of rocks, 

 covered by others, having characters corresponding with those 

 of the Devonian group in Europe. The rocks of the Appa- 

 lachian chain consist of deposits of the Silurian, Devonian, 

 and Carboniferous periods. A deposit called, by the Ameri- 

 can geologists, the Waverley sandstone, which, Mr Lyell is 

 of opinion, corresponds with the old red sandstone of Europe, 

 intervenes in the state of New York between the coal-beds 

 and the Upper Silurian groups, in strata of considerable 

 thickness. On the western side of the Alleghanies, at Ports- 

 mouth on the Ohio, the same formation also occurs, but 

 greatly diminished in thickness, some of the subordinate beds 

 being reduced to a very thin slate, others entirely lost, con- 

 formably with what is observed in other sandstones and asso- 

 ciated slates and shales in that country, viz., by a gradual 

 thinning of the beds as they extend westwani, and as they 

 become more distant from that great eastern continent, now 

 sunk beneath the waters of the Atlantic, frona which the ma- 

 terials composing them must have been derived. 



Our knowledge of the old red sandstone oi* Devonian group 

 has been much advanced by the monograiph of the fishes of 

 that series of deposits by M. Agassiz, which has just been 



