84 Correspondence. 



specific distinctions. This attempt, made mostly by foreign geolo- 

 gists, has been rather hastily extended from classificatory sciences 

 proper — Zoology, Botany, and Mineralogy — to rocks, although the 

 ulterior scientific purpose to which that method is subservient and 

 necessary in those sciences, namely, to ascertain how and to "^hat 

 extent such minute distinctions are fixed or derivative — can scarcely 

 be said to exist in the philosophy of stones, our researches here 

 having pretty well proven that the natural selection which pre- 

 determines the composition of rocks is of the most fortuitous nature. 

 The interest in rocks turns upon other and broader points. Thus, 

 not seeing how the system alluded to is essential to the pursuit of 

 chemical geology, or of mineralogy in rocks, and fully experiencing 

 how great an obstruction it may prove in general geology, it is only 

 upon the faith that no labour is altogether in vain that I can have 

 any tolerance for this new fashion — it may lead to some new 

 development of our glorious science. 



What I would wish to bring to notice is a glaring inconsistency in 

 the use of a familiar English rock -term. In my description of a 

 portion of the N.W. Himalaya, in the Memoirs of the Geological 

 Survey of India, wishing to avoid ambiguity, I defined the sense in 

 which I should use the words schist, slate, and grit. The sanction 

 to which I appealed was, the practise of English field-geologists. 

 Some friendly critic at home took me to task on this point.^ Schist, 

 as implying crystalline foliation (and not argillaceous rocks in 

 general), was allowed to pass. I will not haggle with my objector 

 upon a point of degree in the application of the word slate (and 

 slaty) to subfissile argillaceous rocks, in which that character is not 

 traceable to original lamination ; true cleavage is due to pressiire ; 

 "and so is the imperfect, though important character I would desig- 

 nate as slaty. Upon my use of the word grit I received no quarter. 

 I was perfectly aware at the time that this term was frequently used 

 in a totally different sense to that of my definition ; biit, having 

 served my apprenticeship in Great Britain, I was also pretty sure of 

 my ground when I appealed for sanction to the practice of English 

 field-geologists. During a recent brief visit to England, I did not 

 omit to verify my position. It will, I think, be granted that the 

 classified collections of the Geological Survey of Great Britain and 

 Ireland are a good exponent of the authority I quoted. They are, 

 perhaps, the only named collections in the kingdom that are not 

 based upon a ' Krantzian ' foundation. And in those collections the 

 word grit is frequently, I believe even exclusively, used in the sense 

 I gave to it. I am writing from the Jungles, so cannot refer to the 

 numbers I noted in the printed catalogues of the Museums in 

 Jermyn-street and in Dublin, and which bear the imprimatur of 

 Professors Eamsay and Jukes, but the specimens are easy to be 

 found among the transition rocks. These grits are very fine-grained 

 siliceous rocks ; they appear abundantly associated with slates : their 

 composition and texture is such that in the midst of highly cleaved 



1 See Review of " Memoirs of the Geological Survey of India," vol. iii., Part 2, 

 Geological Magazine, Vol. II. p. 310. 



