38 Rev. A. Sedgwick on the Geological Relations and 



which enable us to connect them together, and, for general purposes of com- 

 parison, to regard them as one group. Great beds of conglomerate coarse sand 

 and sandstone, frequently tinged with red oxyd of iron; and of red marl, asso- 

 ciated with innumerable beds and masses of earthy salts, constitute, in many 

 countries, the principal portion of the group we are considering. Many of these 

 salts, though of almost constant occurrence among the rocks of this epoch, 

 have been developed with so much irregularity, that the attempts to arrange 

 them in distinct formations (when used for any purpose beyond local descrip- 

 tion) have sometimes, perhaps, served to retard rather than to advance our 

 knowledge of the earth's history. The great calcareous beds which were pro- 

 duced during this period form, however, an exception to the last observation. 

 They appear to have been chiefly developed in the upper and lower portions 

 of the system we have been considering; and though possessing some cha- 

 racters in common, are sufficiently distinguished by their position and their 

 fossils to be separated into two distinct formations. The higher of these (the 

 muschel-kalkstcin of the continental geologists) has no representative in the 

 series of rocks which have hitherto been observed in our island; the lower is 

 represented by the great terrace of magnesian limestone which ranges from 

 Nottingham to the mouth of the Tyne*. 



The greatest difficulties in classifying distant portions of the new red sand- 

 stone have not, however, so much arisen out of its mechanical origin and com- 

 plexity of structure, as from its general want of conformity to all the inferior 

 formations. Connected with this fact are three great sources of error. 



1st. Beds of the age of the new red sandstone (even in countries where the 

 successive depositions are complete) may rest indifferently on any of the older 



* If the classification pointed out in the text be correct, the magnesian limestone and the mus. 

 chel./calkstem must be considered as very nearly related. In mineralogical character they also 

 frequently resemble each other. For example, in Dr. Boue's description of the muschel-kalkstein 

 {Journal de Physique^ Mai 1822), it is stated, that cellular beds of yellowish limestone are not 

 unfrequently observed in it, nearly resembling some varieties of the magnesian limestones of En- 

 gland : and the same fact is still more fully confirmed by M. L. Elie de Beaumont, in a Memoir 

 on the secondary formations of the Vosges, which has appeared since the preceding observations 

 were written {Annales des Mines, 1827, p. 450, &c.). But the constancy of position in which the 

 two formations appear, one in the liigher, the other in the lower part of the system with which 

 they are associated, points out a considerable distinction between them, which is made still more 

 perfect by the suites of fossils which respectively belong to them. For the more characteristic fossils 

 of the muschel-kalk {Encrinites monilijormis, Ammonites nodosus, Miftilus socialis, Sec. &c.) 

 are not, I believe, ever found in the magnesian limestone: and in the same way the fossil fish, 

 and the bivalves of the genus Spirifer, and the genus Producta of the magnesian limestone, have 

 not been described among the fossils of the muschel-kalkstein. 



