26 GeoJotiy of tJic Gold Fic/ch of Briiinh, Grtiana. 



Both field and laboratory studies indicate that the foliation is due 

 to the operation of dynamic metaniorphisni. ^4 s a general rule these 

 rocks yield comparatively easily to weathering agencies, and the lower 

 parts of the colony occupied by them consist of level plains or of some- 

 what undulating land. The schistose members of the _group in places 

 show a fissile or a slaty structure and then weather into upstanding 

 slabs. The finer-textured of the massive varieties are often of great 

 hardness and tenacity, and where belts of rock of this description are 

 crossed by the courses of the rivers, rapids and low cataracts occur ; 

 and in these the rocks are angular and rugged — in very marked contrast 

 to the rounded masses which characterise rapids and cataracts caused 

 by the rivers crossing belts of granite or bands of granitoidal gneiss. 

 In the elevated parts of the colony in which rocks of this group are 

 found the surface of the country is often extremely rough, and consists 

 of rugged ridges and mountains, with tabular masses, and in places 

 with jagged pinacles, of rocks protruding from tlie earth, and there 

 forms a rough grass-covered country interspersed with patches of 

 forest. Over the surface of the country frequent patches of blocks 

 ot" the country rock are found, as are others of angular blocks of quartz, 

 and of pebbles derived from the veins of quartz which are common 

 in the altered members of the group. In some parts the quartz- 

 porphyry or the felsite has been completely altered and converted into 

 quartz-rock, this in places occurring as bands of ciuartz-schist. The 

 finer-grained members of these silicitied rocks locally are termed 

 "jasper.'' The most commonly occurring rocks of this series are 

 greyish-green in colour, but their colours vary from diflerent shades 

 of yellow to various ones of grey, green, brown, and black, while some 

 are of shades of red ranging from pale dull red or brownish-red to very 

 bright red. 



The more basic members of this group of rocks are in parts 

 much metamorphosed, giving rise to chloritic or actinolitic rocks 

 frequently of complex composition and confused structure. These are 

 usually of various shades of green, and generally possess a dull earthy 

 appearance. In places chloritic rocks occur, which are of fine texture 

 and have a marked fissile structure ; and these may be metamor- 

 phosed stratified sedimentary rocks, or volcanic tufis. AVhere weather- 

 ing is at all advanced it is only by careful study in field and laboratory 

 that their nature can be made out. Closely connected with the rocks 

 of this group are felsitic mudstones and tufls, which form in places 

 layers in or below the basal beds of the sandstone formation, but 

 these are of very subordinate importance in the lower lying parts of 

 the colony. 



Til". Gneissose Bocks. — Closely allied to the last-described rocks 

 are those forming the basal rocks of the colony ; it is, in fact, possible 

 that the quartz-porphyries and their allies are properly parts of the 

 formation now to be described, and are merely a phase in the 

 earliest geological history of the colony. My investigations in the 

 geology of the colony have led me to the opinion that the porphyries 

 and their allies foiin a distinct phase in its earliest geological history, 



