REMARKS ON THE TERMS PRIMARY, TRANSITION, etC. 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. Tn a former report, 

 I suo-o-ested 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 low^est and oldest in the English series. It is, 

 perhaps, unnecessary to speak in tliis desultorj' 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 arc 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, 



* DifEculties 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. 



