B.Forbes — Geology of Donegal. 13 



subject, as not to entitle theoretical views on the origin of such 

 rocks to any consideration unless they were supported by minera- 

 logical, chemical, or other evidence, of which no trace was to be 

 found in the paper. 



I at the same time took occasion to deprecate a system which I 

 fear has of late become too common : that of rushing off by steam 

 on some hurried trip, often embracing only a few hours' actual work 

 in the field, in order to come back with a paper for some scientific 

 society, crude and undigested, and altogether different from the 

 admirable memoirs to be found in the earlier volumes issued by our 

 Society, when men like Sedgwick, Prestwich, Scrope, our lamented 

 Murchison, and others, devoted, not hours or days, but whole weeks, 

 months, or even years, before appearing in print, and this even when 

 the subject may have been of a far easier nature than one which in- 

 volves perhaps the most intricate of geological problems, the origin 

 of metamorphic and crystalline rocks. 



Passing now to Mr. Green's criticisms : he represents me, in the 

 first place, as laying great stress on authorities ; the very last thing 

 to be expected from me after what I have already written on that 

 subject ; quite the reverse. I quoted Mr. Scott and Prof, Haughton 

 for their observed facts, not for their theoretical opinions ; and a 

 mere reference to their British Association Report on this district 

 (1863, pp. 51, 52, and 53) will prove that they describe the granite 

 as intruding itself into and sending out veins, or dykes crossing, for 

 example, the limestones at Drumnaha and Dunlevy ; hornblendic 

 and quartz rocks at PoUnacally and in Arranmore Island ; and in- 

 closing fragments of other rocks at Bunbeg, Loch Anure, Annagary, 

 Tober keen,. Lough Errig, etc., etc.; the limestone beds being greatly 

 altered at the junction with the granite, exactly as is found to be 

 the case with igneous rocks in general. These facts I know the 

 majority of geologists, at least, will agree with me in considering as 

 ample proofs of the eruptive nature (in contradistinction to the sedi- 

 mentary character) of the granite in question. 



Mr. Green, however, although he informs us he kept his " eyes 

 open," could not observe any instance of its "cutting across the 

 bedding, a thing which was sure to occur somewhere if it were 

 really an intrusive rock " ; a statement which is quite easily ac- 

 counted for if it is remembered how very little of the ground he 

 actually went over in his short visit. His ideas of the nature 

 of foliation (p. 557) would also appear to be somewhat confused, 

 and when he (p. 560) proceeds to state "that a metamorphic rock 

 may be at places intrusive has been explained so often that I am 

 almost ashamed to repeat it," I would still ask him for references to 

 any such explanation which has been accepted by geologists, or to 

 any instances where rocks, originally of undoubted sedimentary 

 origin, have been observed to break through or send out veins or 

 intrusive masses into the neighbouring strata. My excuse for asking 

 this little condescension on his part being, that having myself pub- 

 lished various memoirs (some of which date back more than seven- 

 teen years ago), and having been hard at work in the field and 



