W. M. Hutchmgs — On some Lake- District Rocks. 541 



a matter of individual taste, so many are the systems offered to us. 

 For my own part I think a very much clearer idea of the rocks is 

 conveyed by the more usual method of separate grouping of andesites 

 and basalts (using the name dohrite exclusively for non-vitreous 

 rocks) ; as is exemplified in the classification given by Dr. Hatch 

 (" Introduction to the Study of Petrology "). Various stages of the 

 passage from oue to the other extreme may then be clearly indicated 

 by the use of the adjectives basaltic and andesitic respectively, 

 according to whether we wish to specify an andesite which is 

 tending towards a basalt, or a basalt which is tending towards an 

 andesite.^ 



While on this subject, it is difficult to see why we should retain 

 in use the word " porphyrite " for altered andesites like those of the 

 Lake District. The supposed differences between rocks of different 

 geological age being no longer admitted among English petrologists, 

 and bound to vanish also in Germany sooner or later, why retain 

 any of the names which are connected with the obsolete system of 

 classification, and which appear wholly superfluous when once this 

 is discarded ? As some writer has said, I think, in effect, why 

 should we have a separate name for an old and altered rock, any 

 more than we have a separate name for a man because his hair is 

 grey and his teeth no longer well preserved ? Such names only 

 burden the memory, obscure ideas, and open the way for confusion, 

 because they are so liable to be used in different senses by different 

 writers. It is better, and specially so for younger students, to use 

 two words (or a whole sentence if necessarj' !), and to convey a 

 clear and unmistakeable idea by their means, than to use one word 

 which itself needs a definition attached to it, and very likely has 

 several different ones. "Why should not such words as porphyrite, 

 melaphyre, propylite, and very many more, disappear into the 

 lumber-heap ? They are only a stumbling-block to beginners, and 

 an unnecessary addition to a nomenclature too much burdened with 

 dreadful names in any case. 



The regular types of andesites of the district have in their ground- 

 mass a felspar which shows very small angles of extinction, and 

 sometimes extinguishes parallel. 



It seems tolerably safe to assume that oligoclase largely prevails, 

 and it is very probable that orthoclase is also frequently present. 

 But there are also rocks in which these optical tests show a felspar 

 allied to labradorite to be present in the ground-mass. Labradorite 

 does not appear to be usually recorded as existing in the ground- 

 mass of noi'mally acid andesites. In some of the lavas on Dale 

 Head, etc., examples of it may be seen, lavas which are very full of 

 porphyritic felspars and are unquestionably andesites, 



1 Mr. Teall uses the terra "andesitic dolerite" on several occasions, pointing out 

 that some authors would simply call such rocks augite-andesites ; and he adds the 

 very sensible reminder that "it is a matter of indifference what we call them, 

 provided we recognize their true characters and relations" (British Petrography, 

 pp. 194, 195). 



