TRANSACTIONS OF THE SECTIONS. 61 



That the age of the metamorphic rocks of the Malverns is earlier than that of 

 the Hollybush Sandstone (Middle Lingula-flags) is clear, inasmuch as the latter 

 rests unconformahly on their upturned edges. How much older may be inferred 

 from the fact that between the period of the accumulation of the sediments from 

 which these metamorphic rocks were derived, and that of the overlying sandstone, 

 there took place all those changes which gave to these sediments their crystalline 

 structure, and which involve the lapse of a long interval of time ; for profound me- 

 tamorphism of rocks over a large area is never solely due to the intrusion of erupted 

 masses, but is always the result of a widespread and general cause, t. e., the broad 

 depression of the area to within the influence of the earth's internal heat ; and in 

 this change of level and subsequent reelevation of the area and uptiltiug of the rocks 

 into highly inclined positions, and in their still later invasion by trap-dykes (all of 

 which events were fulfilled prior to the period of the Hollybush Sandstone), we have 

 a measure, as it were, of the length of this interval. 



It is highly probable that the intrusion of some of the associated igneous rocks, 

 as, for instance, the diorite, and possibly some of the granite, may have been contem- 

 poraneous with the metamorphic action ; having taken place into fissures and chasms 

 in the crust while depressed and still in a heated state, judging from their coarsely 

 crystalline condition at their line of contact with the metamorphic rocks, and espe- 

 cially in the small granitic and other veins *. But as regards the trap-dykes, both in 

 the Malvern district and at Mount Sorel, they were evidently of later date, as shown 

 not only by their mode of occurrence, but by their amorphous or minutely crystalline 

 condition at their margins and in their onsets, consequent upon their having come 

 into contact with rocks in a cool state, and capable of rapidly abstracting their "heat 

 of fluidity." 



Whether or not certain associated granitic rocks be metamorphic or igneous, is 

 not now, however, a question for consideration, as iu either case they are equally 

 pre-Cambrian in age. 



As already stated, the metamorphic rocks of the Malverns were upraised prior to 

 the era of the Hollybush Sandstone. They constituted in fact a mountain-range, 

 the crest of a slowly subsiding area of emerged land, during the period in which the 

 Lower Cambrian rocks of Charnwood Forest and the Longmynds were being de- 

 posited, and as this subsidence went on, higher beds were brought consecutively 

 into direct contact with the metamorphic rocks, until finally, at the close of the 

 Lingula-flag epoch, the area may have been nearly or entirely submerged and 

 covered up. There thus occurred a blank in the sequence of sedimentary deposits, 

 the result of the reverse of that change of level which gave rise to metamorphism, 

 and which attends the accumulation of sediments, viz., a local elevation of the crust, 

 and emergence of the area from which the next overlying formation is absent. As 

 these blanks or gaps belong to all ages, it follows there must always have been 

 areas of dry land ; and as the mean sea-level, and therefore the relative proportions 

 of diy land and water, probably never varied very greatly, there must have been 

 emerged land in Lower Cambrian times over areas equal to at least a fifth of the 

 earth's surface, on which no deposition was taking place, forming breaks in the se- 

 quence of formations to which pre-Cambrian rocks formed the floors. From this 

 emerged land were derived the sediments that accumulated in the Cambrian seas. 

 The absence of ^ the Lower Cambrian rocks from the Malvern district, therefore, 

 has no greater significance than the absence of the Carboniferous limestone from 

 beneath the Coal-measures of Bewdley or of Newent, or of the Old Bed Sandstone 

 from the area of North "Wales. 



But at some time after the close of the Lingula-flag period, and between it and 

 the epoch of the May Hill Sandstone, the Malvern area was again elevated, as may 

 be inferred from the total absence of the Llandeilo, Caradoc, and Lower Llandovery 

 rocks, and from the tilted position of the Lingula beds, on the denuded surfaces of 

 which the May Hill Sandstone rests, dipping to the westward at a lower angle than 

 the beds which underlie it. Again,' at the close of the Lower Old Bed Sandstone 

 period, the ridge was upraised, as seen in the absence of the Middle Old Bed Sand- 



* It is equally probable, however, with respect to the diorite, that its coarsely crystalline 

 structure may be due to the action of heat on rocks having the same composition that pre- 

 existed the metamorpliism of the area, ex. gr., traps and some lava beds. 



