14 B. Forbes — Geologij of Donegal. 



laboratory, engaged in the study of tliese rocks for the last twenty 

 years, I am not ashamed to ask for information which I have not 

 been able to find in reliable works on Geology or Petrology, although 

 I have taken great pains to make myself acquainted with the foreign, 

 as well as English, literature of this subject ; and I may further 

 state that a personal acquaintance with many of the most distin- 

 guished foreign authors enables me to assure Mr. Green that they 

 will join me in hojDing that his modesty will not prevent his 

 bringing forward explanatory proofs of views so extremely novel in 

 character. 



Secondly, if Mr. Green does not start with the idea, that the fact 

 of rocks being conformable to other what he calls " undoubtedly 

 bedded" rocks (by which I understand sedimentary strata), is a proof 

 of their being themselves sedimentary ; why does he lay such stress 

 on these points, (p. 55^, and elsewhere,) or why does he require the 

 elaborate section he has brought forward, and which I understood 

 Mr. Scott, in the course of the discussion, not only disputed the 

 correctness of, but even the possibility of its ever having been gone 

 over ; and further to state, with respect to Mr. Green's co-relating 

 the parallelism, of what I maintain are only planes of foliation, with 

 those of true stratification, that the nearest point where '•' undoubtedly 

 bedded," i.e., fossiliferous rocks occurred, was separated by no less 

 than the entire breadth of the county of Tyrone, and most probably 

 had not been visited by Mr. Green. 



As one hard fact is worth a bushel of hypotheses, I would also 

 explain that the specimen of volcanic rock, which I laid on the table 

 at the meeting of the Geological Society when the paper here re- 

 ferred to was read, was neither lava nor slag, but, on the contrary, 

 was as thoroughly crystalline in character as the Donegal rocks ; 

 the parallel structure or foliation in it, being developed by the 

 arrangement of the crystalline components themselves " in parallel 

 layers of various thickness and diiferent mineral composition, grain, 

 and colour," to use Mr. Green's own words, notwithstanding that he 

 employs them (p. 557) as " proofs of its originally bedded nature." 

 Turthermore, it may be added that this rock extends over a vastly 

 greater distance than the section given by Mr. Green ; and that 

 although this gentleman's knowledge of volcanic and other rocks 

 may be so profound as to authorize him stating, " I cannot imagine 

 there is any danger of confounding bedded structure on a large scale 

 with the lamination of such specimens," it may be interesting to 

 him to learn, that outlying positions of this very rock have been 

 mapped by two eminent French geologists, MM. D'Orbigny and 

 Pissis, as beds of sandstones, an error which can only be attributed 

 to their having gone over the country in a very hurried manner, 

 like Mr. Green. 



After the want of appreciation experienced by Mr. Green's paper, 

 it would be rather severe to criticize the jocose style of his con- 

 cluding remarks : but as his information about my habits is evidently 

 only on a par with what he knew of the previous literature of his 

 subject, I would, for his better information, state, that the only 



