162 Dr Boue on the Origin of Tertiary Rocks. 



nate to the coarse marine limestone, sometimes totally indepen- 

 dent, and that it exists as well in the inferior part of the lime- 

 stone as amongst its beds (p. 177.). Now, I ask, if the grey- 

 wacke or the variegated sandstone were called a great formation, 

 it would be allowable to classify under the same head, as great 

 formations, small beds of so subordinate a nature as those beds, 

 or large elliptical nests, of marnO'Charhoneux rocks. These, 

 then, are to be viewed as only a simple dependence or appendix 

 to the Parisian calcaire grossiere or tritonien, of which the first 

 member is the plastic clay, which is only a small local deposit 

 even in the Paris basin, for in the north-western part, a^ near 

 Beauvois, the calcaire grossiere is separated from the chalk by 

 marly sands with green particles. 



This classification will at first view appear rather heretical, 

 although it is very simple, and in accordance with other facts 

 of the same kind. Thus, the sub-apennine clay-marl is covered 

 by sand and shelly limestones. In these last, especially in their 

 under part, there are some argillaceous beds, resembling the mi- 

 caceous sub-apennine clay. No one ever thought of separating 

 these subordinate beds from the sands and the limestone, and 

 forming them into a separate group or terrain. On the con- 

 trary, it is generally acknowledged that these alternations are, 

 as is the case between other deposits, the places of transition or 

 union of one deposit with the other, and that the uppermost 

 argillaceous beds bore less resemblance to the true sub-apennine 

 clay^ and became more mixed with sandy and calcareous parti- 

 cles, and vice versa. Now, is it not exactly the same case with 

 the plastic clay and the argillaceous beds of the Paris limestone, 

 which are sometimes arenaceous and carboniferous ? Is it not 

 natural to suppose that the purest deposit, of clay was followed 

 afterwards at intervals by a more loamy deposit with more cal- 

 careous matter, and entangling lignite, fresh-water shells, &c., 

 while these bodies were accidentally carried into the sea along 

 with the mud of rivers ? Does not M. Brongniart himself con- 

 fess that " la distinction de cette argile (plastique) d'avec son 

 terrain marno-charboneux est quelquefois presq' impossible '' — 

 p. 199.) ; that, besides the mineralogical difference between both 

 is trifling (p. 177.), and that they contain the same minerals, 

 the selenite, pyrites, &c. ? Lastly, does he not expressly say. 



