1814.] on Transition Rocks. 28f 



shall in the first place state as clearly as I can the point or points 

 mainly at issue betwixt Mr. Allan and me. 



The object of his paper, entitled " Remarks on the Tran- 

 sition Rocks of Werner," was, 1 conceive, chiefly to estabh'sh 

 the following propositions. First, " that the killas of Cornwall, 

 (that is, according to him, the rock which lies iv.m'-diately on 

 tlie granite of that county,) belongs to the transition series of 

 Werner." Secondly, " that tlie granite of Cornwall is pos- 

 sessed of every character by which the oldest vaneiies are dis- 

 tinguii^hed." And thirdly, that " that granite wliicli forms the 

 nucleus round which Werner conceives all other rocks were depo- 

 sited," (that is, the first granite formation,) " is in some cases 

 actually of a later date than the transition series." The object of 

 my paper again was to show that Mr. Allan had failed in proving 

 his point ; and that the arguments he employed for the purpose 

 would not bear the test of examination. I showed that he had 

 mistaken or mistated the writings of Professor Jameson, and had 

 not reasoned correctly either from his own observations, or from 

 those made by others. Let us now see whether Mr. Allan in his 

 answer has said any thing to invalidate what I maintained. In 

 page 27"> of his Elements of Geognosy, Professor Jameson has the 

 following sentence: "Molybdena, menachine, tin, scheele, cerium, 

 tantalum, uran, chrome, and bismuth, are metals of the oldest 

 primitive formation, and only feeble traces of them are to be ob- 

 served in newer periods." This sentence Mr. Allan quotes to 

 prove that, according to Professor Jameson, tin is to be found 

 only in the oldest primitive rocks. Such, however, is certainly not 

 the Professor's meaning. Oldest }^x\m\\\\e J'ormalioii does not here 

 signify the oldest primitive rock. It signifies the oldest repository 

 of the metal. And everv body knows that a metal may occur in 

 veins even in the oldest granite, and yet be newer than when 

 disseminated through clay-slate. 



In page 2G1 of his Elements, Professor Jameson says of tin, 

 that " it occurs In very old veins that traverse granite, gneiss, 

 mica-slatc, and clay-slate." Mr. Allan asks me, " whether I sup- 

 pose that this granite, connected with gneiss, is that belonging to 

 the newest formation, alluded to in a subsequent paragraph of the 

 same page." My answer is that I do ; and for the fullovving rea- 

 sons. The Professor says; "tin is of nearly contemporaneous 

 origin with old primitive rock>;. Thus it occurs in very old veins 

 that traverse granite, gneiss, uiica-slate, and clay-slate." Had he 

 meant the oldest granite, lie vvould have said not old but the oldest 

 primitive rocks. And that he did not mean the oldest granite is 

 evident from the next paragraph, where he says, that " tin occurs 

 disseminated through granite, and In beds that alternate with strata 

 of granite ;" and that " this granite aj^pears to belong to tlie newest 

 tormaiion." As to the connexion of this granite with gneiss, 

 alluded tu by Mr. Allan, I beg leave to refer him to Profcsior 



