438 Notices respecting New Books. 



entitled to conclude, that in a given district the age and position of 

 certain strata, or groups of strata, are infallibly indicated by their 

 organic contents. These researches, commenced by Mr. Smith in 

 England, have been extended with the same results over all parts 

 of Europe, and a large portion of America, and therefore it is con- 

 cluded that strata, or groups of strata, are to be discriminated in 

 local regions, and identified in distant countries, by their imbedded 

 organic remains. 



" Having thus obtained the general principle, let us endeavour 

 to ascertain the extent of its applicability, and the precautions ne- 

 cessary to ensure accurate results. 



" So unequally are the different species of fossils distributed in 

 the earth, that, whilst some are dispersed through several neigh- 

 bouring strata, as Clypeus clunicularis among the oolitic rocks, 

 others are confined to one stratum, as Ammonites calloviensis to 

 the Kelloways rock, and some to a particular bed of stone, as the 

 Astreae which characterize the coralline oolite. 



" It is therefore possible, by collecting numerous specimens 

 procured from a limited district, to assign to each formation of strata, 

 single stratum, or even characteristic bed of stone, all the fossils 

 which have ever been discovered in it. Such catalogues being com- 

 pared, formations, strata, and beds, may be found to differ from one 

 another by the presence or absence of particular species. A given 

 formation may possess species never found in any of those above, 

 and it may be deficient in others which do occur above, and in like 

 manner it may differ from those below. Hence it may be con- 

 cluded, 



" 1. That a formation or stratum may differ from all those above 

 it, by the presence or absence of certain species, and from all those 

 below it, by the presence or absence of other species : 



" 2. That it may contain some particular species, unknown either 

 above or below. We may add, that formations and strata may differ 

 by the relative abundance or paucity of their imbedded fossils. 



"EXAMPLES. 



" 1. The coralline oolite formation, as defined p. 32, appears to 

 me to differ from all the formations above, by the presence of Am- 

 monites perarmatus, Mya literata, and Clypeus clunicularis, and by 

 the absence of Ostrea delta, hamites, and ananchytes ; and from all 

 those below, by the presence of Spatangus ovalis ? and Ammonites 

 perarmatus, and the absence of Productae, Axini, Ammonites Wal- 

 cottii, Nerita costata, Astarte minima, and Terebratula digona. 



" 2. Again, the Kelloways rock differs from all the strata above 

 it and below it, by the presence of Ammonites calloviensis, and Gry- 

 phaea dilatata : no stratum in Yorkshire but the Kimmeridge clay 

 contains Ostrea delta ; nor is Gryphaea incurav found except in lias 

 beds or lias boulders. 



" 3. It is in the lower part of the coralline oolite that Clypeus 

 dimidiatus, and C. clunicularis abound, but Melania striata belongs 

 to the upper layers of that rock. 



" These are the principles of investigation which it is proposed to 



apply 



