Geological Society. 55 



I must remark, that in the triple classification of the tertiary forma- 

 tions, the author errs in supposing that the shells of our crag, which 

 he identifies with his upper marine, are all of existing species ; it 

 being ascertained that the crag contains only about 45 per cent, of 

 shells identical with those now living. 



Nor can the middle tertiary formation of Mr. Conrad be positively 

 identified with the " calcaire grossier," until we are supplied with 

 lists of the relative numbers of the existing and extinct species. The 

 lower tertiary formation, it is evident, cannot be classed with the " ar- 

 gile plastique" of M. Brongniart, upon the test of lignite alone ; since 

 that substance is no longer deemed characteristic of one particular pe- 

 riod, but occurs in tertiary groups of all ages : in truth, the plastic clay 

 occupies no longer a place in the list of European formations, being 

 simply the occasional substratum of certain tertiary basins, in many 

 of which it is inseparable from the overlying clay. These errors of 

 comparison and geological classification are, however, quite excusable 

 on the part of a naturalist, who strives to arrange his subject after 

 models he has been taught to consider classical, but which inevitably 

 have partaken of such defects as characterize the broad generali- 

 zations of the early geologists of all countries. Such defects are, 

 however, of little moment, and can soon be obviated. The high merits 

 of the undertaking of Mr. Conrad are to be found in an accurate de- 

 lineation of the organic remains, and in his faithful account of the 

 manner in which the strata containing them have succeeded to each 

 other. By his description we now learn, for the first time, that the 

 whole line of coast of North America has been elevated after the 

 creation of existing mollusca, and that the highest or youngest of 

 these fossil groups is spread over a zone of land of 150 miles in 

 breadth ! Judging from the information before us in the first fasciculus 

 of this interesting work, it may be inferred that these upper shelly 

 sands and marls are synchronous with those modern elevated groups 

 in the Mediterranean, by some geologists termed Quaternary, which 

 Mr. Lyell classes in the group of newer Pliocene. I have now to ex- 

 press my hope that Mr. Conrad may meet with such encouragement, 

 that he may complete not only the illustration of these younger and 

 tertiary shells, but succeed also in his laudable ambition of describing 

 the remains of the secondary and older formations of North America. 

 That geology is pursued with vigour in other States of the Union, 

 we have abundant proof in the Journal of Professor Silliman. 



Professor Hitchcock has published a well-digested and circumstan- 

 tial Report upon the Mineral Structure of Massachusetts, accompa- 

 nied by an illustrative map. That part of the work which shows the 

 value of an acquaintance with mineral masses in their application to 

 the agriculture and commerce of the State, has alone appeared j but 

 the materials, therein collected, bear testimony to so much ability and 

 research, that some good geological induction may be looked for in 

 the second volume. 



This author will, however, pardon me if I suggest some caution in 

 the identification of those great tracts of red sandstone in America 

 with the new red sandstone of England ; since it is obvious that in 



