210 J. B. Hill — The Palwozoics of West Cornwall. 



westward is in contact with the Lizard group. Besides this main 

 outcrop small infolds also occur amongst the Veryan Series. Litho- 

 logically, the group consists of conglomerate, sandstone, and clay 

 slate, the two latter being often calcareous, and they are all so 

 clearly interbedded that their natural sequence is obvious. The 

 most important member is undoubtedly the conglomerate, from 

 the evidence it affords of the derivation of the group. Its character 

 and main constituents have been given in a former publication,' since 

 which it has yielded chert, mica - schist, and possibly serpentine. 

 The latter ingredient, however, being obtained from a road section, 

 the evidence is possibly not conclusive. At its northern margin, 

 where the conglomerate is in close relation with the Portscatho 

 Series, it is almost entirely composed of fragments derived from that 

 group. This is admirably exhibited at Gillan harbour, where the 

 magnitude of the boulders, often exceeding a foot in size, enables 

 their ready identification with the Portscatho Beds in their immediate 

 vicinity, in which practically every type of the latter is seen to be 

 incorporated. The fact, moreover, that the fragments were veined 

 with quartz prior to such incorporation sufficiently indicates the 

 magnitude of the break represented by this unconformity. The 

 conglomerate is likewise seen in contact with the Portscatho Beds 

 on the coastal shelves at Men-aver Point and Nare Point. It has 

 been remarked that the conglomerate varies with the nature of the 

 underlying rock from which it is derived. Whereas at Gillan Creek, 

 where it rests on the Portscatho Series, fragments of that group 

 preponderate, as the Veryan Series and quartzite horizons are 

 approached it partakes more of the character of those types, and the 

 foreign fragments derived from the Lizard rocks increase in a similar 

 direction. The conglomerate is by no means continuous, but the 

 base of the formation is frequently of fine texture. This is shown 

 by the protruding bosses of quartzite, some of which are encircled by 

 the sandstone beds of the Manaccan Series. There is, moreover, 

 a tendency for the coarser deposits to die out in a westerly direction, 

 as was long ago recorded by De la Beche,- the frequent absence of 

 which presents difficulties in the demarcation of the Manaccan Series 

 from the older Palaeozoics that underlie them, and especially where 

 good sections are not available. 



The Manaccan Series present a less advanced type of metamorphism 

 than that of the Lower Palaeozoic divisions amongst which they 

 occur. This difference in deformation between the older and newer 

 Palaeozoics, although not always of a very marked type, was early 

 recognized by the author as a significant factor, more especially in 

 the comparison of the killas of Mid Cornwall with that occupying 

 the western regions, which pointed to the conclusion that the latter 

 represented conditions of stress that were either not experienced 

 by the former or prevailed in a less vigorous degree. In the 

 Manaccan area this contrast is admirably illustrated by the com- 

 paratively unaltered condition of the clay slates associated with the 



» J. B. Hill: Trans. Koy. Geol. Soc. Cornwall, 1901. 



2 " Eeport on the Geology of Cornwall, Devon, and West Somerset,'" 95. 



