REMARKS ON THE TERMS PRIMARY, TRANSITION, OtC. 
21 
or it is imperfectly defined in consequence of the operation of causes, of which I shall have 
occasion to speak in the sequel. Our views may be simplified still farther, by imagining 
the entire primary mass as having been formerly an island, around whose borders the sedi¬ 
mentary rocks were deposited; and as we recede from those ancient shores, whether to the 
north, east, south, or west, we pass from the older to the newer deposits. In a former report, 
I suggested that the Potsdam sandstone, which rests in this district upon the primary, is one 
of the oldest sedimentary rocks of the globe. This view seems to be borne out by the fact, 
that it underlies all the rocks of the Silurian and Cambrian systems, if we leave out of view 
those which are called metamorphic. 
All the observations upon this rock have resulted in establishing the fact, that it is beneath 
the Cambrian system of rocks, which are the lowest and oldest in the English series. It is, 
perhaps, unnecessary to speak in this desultory way of those rocks, which are to be the 
special subjects of remark. I do so merely for the purpose of showing the sudden transition 
from the highly crystalline rocks to those which are merely earthy deposits, and which are 
composed of the abraded particles from previously existing masses. 
The classification which I propose to adopt in this report, is that which appears to be ge¬ 
nerally approved of, and followed in this country, viz. that which places the rocks under the 
following heads : Primary^ Transition, Secondary, Tertiary. I can see no valid objection 
to retaining those names for the first and great divisions, though I am aware that they are not 
in repute with many who sway public opinion ; still, so far as substitutes have been proposed, 
they appear to me quite as objectionable as the old terms. The truth is, so long as descriptive 
names are inapplicable, and since rocks coalesce or graduate into each other, so much so at 
least as to prevent our drawing lines of distinction between adjacent masses, it appears bet¬ 
ter to retain those names which have become familiar, if not classical, than to encumber 
the science with those which are new. Take, for illustration, the terms transition and 
Silurian : the former is said to be objectionable for two reasons ; the first is, that the limits of 
the rocks which have been classed under the word, have not been settled. Admitting the 
fact, has not the extent and meaning of the word silurian to be determined arbitrarily ? Is it 
then not a question whether it shall include the beds of passage from the Silurian rocks into 
Old Red or Devonian system ?* If so, then the same objections apply equally to both. The other 
objection to the word transition, is, that it involves theoretical views which are questionable ; 
but who ever, nowadays, thinks of the theory which led to the selection of this word as a name 
for a class of rocks. If only those names were to be rejected to which this objection applies, 
science would be thrown at once into a state of confusion and disorder ; for more than one half 
of the names of things in natural history have been given under notions as erroneous as the 
word transition ; but it does not follow that the error which led to the selection of the name. 
* Difficulties as great, if not greater, meet us in defining the limits of the silurian and Cambrian rocks ; in fact, the Cambrian 
appear to be, in part, silurian. In addition to these objectionable points in the general use of those words, we have rocks highly 
fossiliferous which do not belong to either system, as they now stand defined. 
