182 Correspondence. 



Some gneiss will be equally well proved to be of igneous origin;^ 

 nay, even masses of crystalline limestone must frequently be classed 

 as igneous rock. 



It is needless, however, that I should follow Mr. Forbes into all 

 the minute criticism which he has thought proper to bestow upon 

 my papers. He remarks that " the crystallographer will be rather 

 puzzled" with my somewhat careless expression, porp/ii/niic felspar 

 crystals; if so, it will not argue much for the crystallographer's 

 penetration. 



The writer concludes his remarks by disclaiming " any feeling of 

 personality against a gentleman whom he has never even seen." Surely 

 in a discussion of this kind, such a disclaimer ought to be quite un- 

 necessary. Personalities are here utterly out of place, and I would, 

 with deference, submit that personal details are equally so. Is it 

 not beside the question altogether, that a gentleman so well known 

 as Mr. Forbes should tell his readers that he " does not speak upon 

 the strength of an acquaintance with this subject of a few months 

 or years, but for more than twenty years has continuously occupied 

 himself in a special and minute study of the crystalline and meta- 

 morphie rocks ;" that he should assure us that he has examined these 

 rocks "in the field over a great part of Europe, North and South 

 America, Polynesia, part of Africa, etc., with all requisite appliances 

 at his command, and without having neglected the study of chemis- 

 try and mineralogy ;" that besides pressing upon us the fact of his 

 being a qualified chemist, mineralogist, and petrologist, he should 

 be at the trouble to point out that he knows how to handle the 

 microscope, and that he has gathered together " above 900 sections 

 of crystalline and metamorphic rocks from about 480 localities, in 

 difierent parts of the world ;" that, in addition to all this, we should 

 be informed that he is well acquainted with " the English, French, 

 German, Spanish, Italian, Swedish, and Danish languages ?" Surely 

 the many memoirs and articles contributed by Mr. D. Forbes to 

 British and foreign scientific publications ought to testify enough 

 to his rare opportunities for observation, and be sufficient guarantee 

 of his accomplishments. 



I am. Sir, faithfully yours, 



Jas. Geikib. 

 Edinburgh, February/ 20th, 1867. 



FAULTS IN DUIFT. 

 To the Editor of the Geological Magazine. 



Deab Sir. — As the subject of faults in the Drift has been before 

 your readers for some time past, I venture to send you a sketch, 

 taken a few months since at Eochdale, in Lancashire, during the 

 progress of excavations for the new Town Hall. Though personally 

 inclined to be incredulous regarding the occurrence of faults in these 

 deposits, knowing how subject they are to sundry irregularities of 



' I am well aware that some geologists are fully persuaded of the igneous and 

 eruptive character of certain gneissic rocks. 



