1814.] oft Transilioyi Rocks. US 



contradiction not only to what 1 have above quoted, but what he 

 himself mentions in his second volume, p. 387.* Under the 

 geognostic situation of tin, he states — " It occurs o7iIi/ in primitwe 

 rocks, as granite, gneiss, ike. and is the oldest of all tke metah." 

 And p. 490, of wolfram — " It occurs in primitive mountains, and 

 in the oldest formations. It is almost always accompanied witli 

 tin." This I conceive to be quite suflici. nt authority for the state- 

 ment I ventured to make respecting the age of these metals, and 

 to warrant me entirely in saying, that as they were considered in 

 other countries indicative of the oldest primitive formations, the 

 Kime inference must apply to their occurrence in Britain. 



Dr. Grierson having, in his own opinion, successfully reduced 

 the age of these tv.-o metals to the period of tlic transition series, 

 now proceeds to subvert my statements respecting the antiquity of 

 the granite itself. In comparing what is stated by Professor 

 Jameson on that subject with the nature of the rock I met with in 

 Cornwall, 1 found the cliaracters attributed to the oldest granite to 

 coincide exactly with tiie granite I found in Cornwall ; and I have 

 stated, with tolerable distinctness, that such was the general 

 appearance it presented throughout the country. This, however, 

 is the same granite that penetrates in veins tlie killas of Cornwall, 

 and in doing so is frequently found to contain fragments of the 

 «tratitied rock. " Who ever heard of fragments being found in 

 the first granite formation ? " is the exclamation which escapes Dr. 

 Grierson on the occurrence of this assertion. All I have in answer to 

 say is, that the granite of Cornwall, presenting the characters of tlie 

 most ancient varieties of that rock, according to the authority of 

 Werner himself, as given by Mr. Jameson, does contain, iti the 

 veins which extend from it, abundance of fragments. This fact has 

 subsequently been verified by yourself during your examination of 

 St. Michael's Mount. 



Dr. Grierson asserts, that among my other inaccuracies, I have 

 given it as a Wernerian principle, that primitive rocks contain no 

 mechanical deposits ; and mentions, as a proof of his j)osition, 

 that according to Jameson conglomerates are found in primitive 

 countries. Now, although a conglomerate should be found in 

 a primitive country, I am not quite certain wlicther that would 

 constitute a primitive rock. In the second place, although it be 

 quite true that Professor Jameson has mentioned this substance as 

 occurring in his primitive porphyry-suite, I cantiot comprehend 

 how a rock formed of fragments of other rocks can be supposed to 

 be of primitive formation ; and, in the third place, the only refer- 

 ence that I have made to this subject is by stating, that from granite 

 down to clay slate no detritus, dr any thing like organised bodies, 

 was to be observed; and according to Mr. Jameson (p. G8) I might 



• The proper inference would have been that Professor .Jamc«on had altered iiii 

 •pillion; for hib third voluiuv \va> piiblitiicd some yeiirs afit;r his second.—^. 



Vol. III. N" II. II 



