118 On the Modes of identifying the Strata, 
to select many individual Shells from the very same Bed, in dif- 
ferent Places, as | have recommended above: and if reliance could 
alone be had on Maps for identifying the Beds, this certainly 
would at present be a fatal objection to my proposal; but the 
case is otherwise, because in most instances, the number of or- 
ganic Species is so considerable, in each of the assemblages of 
Strata to which Mr. Smith has given Names and Colours on his 
Map, and amongst these numbers of Species, there are mostly, 
so many which possess such strikingly distinct characters, as to 
place them beyond all manner of doubt: and these characteristic 
Species, being first sought for, in the Beds of every Quarry or 
Cliff which is examined for collecting Specimens for descrip- 
tion, the relative situation above or below, and often both above 
and below the Beds, of some of these characteristic Species, may 
be ascertained, and used as the means of identifying the Bed of 
an ambiguous or doubtful Species: first through the whole cireuit 
or length of the Quarry or Cliff under examination, next of the 
nearest adjacent Quarries or Cliffs, wherein the same characte- 
-ristie and doubtful Species can be traced, and then progressively, 
to other more distant Quarries or Cliffs, until at length, the 
greatest range of observation is obtained, which our Island admits. 
And besides which, important helps may often be obtained, 
from the mineral characters and qualities of the Beds containing 
doubtful Species, or from those characters in other Beds, which 
underlie or overlie them: but until such time as the present fa- 
shionable notions of the existence of universal Formations or 
strata composed throughout of the same precise Mineral Species, 
have subsided, I would, from my experience, beg to recommend 
considerable caution, in making these appeals to the Mineral cha- 
racters of the Beds, in the consideration of their Organized Remains. 
Because I mean to maintain, that éhe Afineral characters cannot 
safely be relied on, without the concurrent support, of ¢racing 
the same individual Bed or Mass, as has been done in the gross 
by Mr. Smith in his Map of England, as has more perfectly been 
done in my large Manuscript Map of Derbyshire, and in others of 
smallerextent, and as may with ease and certainty be done, through 
the extent of most Quarries or Cliffs*; or by the concurrence of 
*Tn ‘the doing of which, it will often be perceived, that very great and 
complete mineral changes take place, in the same bed or mass, within a 
very smal! distance: sometimes these changes appear to be abrupt, and at 
others gradual: for instance, I have lately seen in this town, a moderate 
‘sized cabinet specimen, brought from the SSW. side of Shap in Westmore- 
Jand, one end of which is Basalt, and the other such highly crystalline and 
large grained Granite,as if shown detached, could not fail to be pronounced 
by any Geognost, as part of a primitive mass ; and such, indeed, the mass 
whence this specimen was broken, has often been pronounced, yet without 
this opinion gaining universal assent. See your 50th volume, pp. 361, r 
the 
