PRE-CAMBRIAN ROCKS OF NEWFOUNDLAND 471 



grains of quartz, fresh plagioclase, orthoclase, and rhyolite and 

 granophyre, with rarely a fragment of basalt. Accessory minerals 

 comprise grains of primary epidote and occasionally abundant 

 grains of magnetite. A film of hematite coats each grain, and in 

 some specimens the interstices are filled with secondary quartz, 

 sericite, or occasionally with epidote. The sericite is a secondary 

 product, the result of recrystallization during shearing. In one 

 section a rounded grain of primary epidote is coated with a film 

 of hematite and is surrounded on the outside of this by a growth of 

 secondary epidote. The cement of the green sandstone seems to be 

 of an epidotic nature, apparently arising through a recrystallization 

 of an impure argillaceous material. A chemical analysis of the 

 reddish-brown sandstone serves to confirm the highly feldspathic 

 nature of this rock. 



TABLE IV 



Chemical Analysis of Feldspathic Brown Sandstone from 



NEAR Signal Hill, St. John's 



Si02 71.38 Na^O 2.28 



AI2O3 14-25 K2O 1 . 99 



Fe203 4.75 H2O+ 1 . 20 



FeO.... 46 H2O- 21 



MgO 46 



CaO 3.01 Total 99-99 



That the red color of the brown sandstones is due to hematite 

 and to the oxidation of its iron content is evident from a comparison 

 of the ferrous and ferric contents of the red and green sandstones. 

 Although both have similar total contents of iron, 4 . 74 and 5 . 11 

 per cent respectively, expressed in terms of ferrous iron, the brown 

 sandstone shows 4.75 per cent of ferric oxide and only o . 46 per cent 

 of ferrous oxide, whereas the green sandstone shows 2 . 54 per cent 

 of ferric oxide and 2 .82 per cent of ferrous oxide. 



The red color of the sandstones depends in varying degrees upon 

 the primary deposition of a hematitic mud in the interstices of the 

 sand grains; upon the deposition of hematite as a cement around 

 the sand grains; upon hematite existing in the grains themselves 

 as in the cleavage cracks of feldspar, or in oxidized basalt and rhyo- 

 lite; and upon the hematite resulting from the oxidation of 

 magnetite grains in situ. 



