^. i: I 



530 



i;i.ruuT--^l884. 



m 



m 



1 ■ ; 



ill 



fl ill: 



only to clL'avtd loclis of distinctly detrital, more oi* less argillaceous 

 materials. 



(A) England. 



(1.) GorniK'nV : Tlf Li'r.nrJ Rerjion. — A considerable portion of the 

 peninsula south of the Ilelford river consists of metamorphic stratified 

 rocks, which arc well displayed in the fine cliffs foi'ining its picturesque 

 coast; iidaiid, as a rule, exposures are few. The neighbourhood of the 

 Lizard Point is the only po.rt where a comphite and continuous section is 

 obtained, as musses of intrusive roek oecn])y no small portion of the 

 district, and frerpiently rise directly from the sea. The metamorphic 

 (stratified rocks may be divided into three groups, between w' ich, how- 

 ever, there does not appear to be any very sharp line of (^ arcatioii 

 mineralogically, or any reason to suppose a discontinuity. .Siiil, as each 

 is distinguished by marked and dominant mineral characteristics, it is 

 convenient to describe them separately. 



There is a good deal of rolling, much disturbance from the intrusion 

 of igneous roek, and faults are numerous in this district ; but probably 

 there are no very vast dislocations, and there are no indications of sharp 

 flexures on a large scale, or overthrows such as arc frequent in districts 

 which are or have been mountainous, so that it seems safe to follow tlie 

 ordinary princijdes of lowland stratigraphy in working out the geology. 

 Enumerating the groups in ascending orders, we have — 



(«) Mic(tre(iii--' Grovp : characterised by rather compact dull green 

 schists, wjiose exact mineral composition cannot be readily decided 

 in the Held, and by I)ro\\uish mica-schists. These, as a. rule, are com- 

 posed of very minute constituents, moderately fissile, sometimes witii a 

 slightly ' llinty fracture,' not seldom very beautifully corrugated on a 

 small .scale. The rocks, though the constituent minerals are in niiiiiv 

 e'as(>s very small (considerably less than •01" diameter), are completely 

 metamorphosed. The green schists, on microscopic examination, are seen 

 to be com[)Oscd of an acicular light green variety of hornblende, of a green 

 fdmy mica, or pei-haps in some cases a chlorite, of quartz, of a Jittle 

 magnetite, ha'matite, or pyrite, with ejddote, a coloui-less gai-net (rare). 

 :ind a kaolin like mineral perhaps replacing felspar. The green minerals 

 and quartz are, however, the dominant constituents, so that the imnic 

 'Taleomieaeeous,' which was a.ssigned to the series by De la Beche,' \ya> 

 macro.scopically appropriate, although, strictly speaking, there docs not 

 appear to be ariv true talc. With it, but not largely developed, occurs !i 

 brownish, slightly silvery mica-schist, in one place more coarsely 

 crystalline than the above, consisting chietly of brown and green mica.s 

 (probably biotite and its alteration products), and paragonite (r), witli 

 quartz and a few small garnets. This group, as stated, is well exposed 

 in the .southern cliffs of the Lizard from a short distance to the north of tlio 

 Quadrant Headland to the neighbourhood of the Lighthouse. Its strike 

 is roughly from WNW. to ESE., with a dip on the northerly side, bat 

 there are many minor twists and rolls. The same group is exposed for 

 a vei'y limited extent in the cliffs on the south side of Porthalla Cove.' 



(i) JIi)nihle)idic Group. — This group is much more extensively de- 

 veloped than the former in the cliffs forming the eastern and western 

 faces of the Lizard peninsula, and a considerably greater vertical thick- 



' llrpoH on the (Ivoloijy of Ci>r»>vall avtl Ikron, p. 2D. 



'■^ As.-ociatcd with this is a band, a few foot thick, of ii granitoid rock ; it may ix" 

 an intrusive vcin-yraiiite modified by compression, but looks as if il were interbeddcd. 



