Tol. 57.] AMONG THE MALVERN CAMBRIANS. 183 



subordinate type. To these belong a series of ophitic olivine- 

 diabases ; a related series of porpbyritic olivine-basalts ; and a series 

 of amphibole-bearing porpbyritic rocks, probably to be regarded as 

 camptonites. These types are not connected by intermediate 

 gradations ; all three show a different distribution ; and the oli vine- 

 bearing and the amphibole-bearing rocks have a different mode of 

 occurrence. According to existing analyses the former range in 

 chemical composition from thoroughly basic to ultrabasic ; the 

 latter are generally more acid, and include sub-basic varieties. 



The rocks appear to find their nearest analogues in the 

 camptonitic ' diorites ' of Warwickshire and other parts of the 

 British Islands, and like these occur only in association with 

 Cambrian rocks ; but the whole assemblage has the stamp of a local 

 character. The Warwickshire rocks, to a certain extent, appear to 

 bridge over the gap which exists between the Malvern Amphibole- 

 bearing Series and the Olivine-bearing Series. 



Intrusion took place in times later than the deposition of the 

 Tremadoc Beds of the Malvern district, and probably earlier than 

 that of the Upper May Hill Sandstone. 



In conclusion I would express my sincere thanks to Prof. Watts 

 and Prof. Sollas, who have given me the benefit of their opinions on 

 some of the more obscure rocks. To Mr. Cecil Duncan I am 

 indebted for the determination of the percentage of silica in one of 

 the rocks ; to Prof. G. Paton for kind assistance in photographing 

 some of the rocks ; to Mr. G. T. Prior for references to the 

 literature of the subject, and much courtesy shown to me during 

 my examination of the rocks in the Allport Collection ; and to 

 Mr, H. D. Acland for the kind loan of rock-sections. 



EXPLANATION OF PLATE VII. 



Fig. L Portion of the marginal facies of oliviue-diabaae (M 182e), 

 showing small phenocrysts of felspar in a groundinass containing 

 minute laths of felspar, etc. X 72. 



2. Olivine-basalt (M 214), showing a group of phenocrysts of aerpen- 



tinized olivine in a groundraass of felspar-laths, augite, ilmenite, etc. 

 X 15. 



3. Olivine-basalt (M214) with a small group of phenocrysts (after 



olivine), in a groundmass showing clearly the augite- and felspar- 

 microlites and iron-ores, X 33. 



4. Olivine-baealt (M249). Portion of the groundmass showing felspar- 



lalhs, some very jBbrous ; needles of apatite ; iron-ores ; and patches 

 of serpentine, probably after augite. X 67. 



5. Andesitic camptonite (M 101a), showing dark bastite-and- 



serpentine-pseudomorphs after araphibole, set in a fine-grained 

 groundmass. Most of the small dark patches seen are sections of 

 needles of amphibole, but a stout phenocryst is shown at the bottom 

 of the figure. X 10. 



6. Andesitic camptonite (M439a), showing long and sometimes 



interpenetratiug crystals of nearly colourless araphibole, with a 

 resorbed border. X 16. 



