Dr. Irving — The Malvern Crydallinps. 455 



doubtful cases are mentioned by Mr. Eutley.^ He considers, there- 

 fore, that evidence is wanting of any volcanic rochs ^ [stricto sensu) 

 ill the Malvern Chain, except those of a later date recognized as 

 Pebidian on the flank of the Hereford Beacon. In some parts of 

 the range a rough parallelism can be observed betvs^een the dykes, 

 and the prevalent trend seems to be N.W. and SE. ; but there are 

 many exceptions to the rule, and they have had very little to do 

 with determining the present contours of the hill-flanks.^ In some 

 cases they have acquired a slabby structure, as if from roughly 

 parallel divisional planes produced by shrinkage during the final 

 stage of their solidification. Their intrusive relation to the Granite- 

 diorite series seems to be established by (i.) their dyke-like form 

 with boundary-walls often extremely well-defined;* (ii.) the in- 

 clusion in them of masses of the older series (such inclusions 

 consisting of granite, or of diorite, or of diorite veined with 

 felspathic material) ; and in one instance (in an old quarry at 

 North Malvern at the extreme end of the range) a large inclusion 

 of hornblendic rock is seen to be itself previously intersected by 

 felsitic veins, which are truncated ofi^ abruptly at the boundary of 

 the enclosed mass,* pointing to an earlier date for the intrusion of 

 the felsite. The enveloping dolerite itself has here acquired a 

 slabby curvature, as if from the resistance of the included mass 

 producing internal stresses in the dolerite during its solidification. 

 North Hill, Worcester Beacon (near the summit and in the higher 

 parts of Rushy Vallej'^ on its lower eastern flank), the quarry at the 

 N.W. corner of Swinyard Hill, the Gullet Quarry, the Wych Eoad, 

 and St. Anne's W^ell, are some localities, where this dyke-relation 

 seems clear. These intrusive masses appear to be portions of a 

 deeper magma, which (first the acid, then the more basic portions) 

 simply flowed into great fissures of the Granite-diorite series, as the 



1 « On the Rocks of the Malvern Hills," Q.J.G.S. August, 1887. 



- The extended sense in which this term has been lately applied by Sir A. Geikie, 

 in his two Presidential Addresses to the Geological Society, is much to be deprecated, 

 from the confusion of thought it is likely to engender and the violence done to the 

 literature of petrography. The term " volcanic " is used as equivalent to " igneous," 

 and the term "eruptive " is made to do duty for " plutonic." In this way the Lewisian 

 gneiss is included in his volcanic series (1891 Address, p. 32). Introduce the pressure 

 of the Archaean atmosphere, and all the facts on p. 33 tell the other way. To speak 

 of such rocks as tourmaline-granite as parts of a great "eruptive-stock," as Credner 

 [loc. cit.) does of the more deep-seated but unerupted igneous masses at Predazzo 

 and Monzoni, is one thing ; but to take the great Archaean gneiss series by themselves 

 and label them "eruptive" or "volcanic," when there is no evidence whatever of 

 lava-flows or tuffs to connect their history with what is usually understood by 

 vulcanicity, is another thing altogether. 



^ Dr. HoU seems to have generalized rather hastily on this point. See Q..J.G.S. 

 vol. xxi. pp. 72, et seq. " On the Geological Structure of the Malvern Hills, etc." 



* Excellent examples may be cited from the Worcester Beacon and its flanks. 

 One bold crag high up the south flank of Rushy Valley is half granite, half dolerite, 

 the latter much crushed and brecciated, with a trace of cleavage here and there. 

 The junction is unmistakable both on the north-looking vertical face of the crag and 

 on the ground-plan above. 



* In this and some other cases the included mass seems not improbably to have 

 fallen into the later and more basic magma, and to have floated off after the manner 

 of some of the masses described by Dr. A. C. Lavvson in the Rainy Lake Region. 



