187 



It is not a region that can be easily mapped in a geo- 

 logical sense. The sediments spread over its surface are 

 relatively thin, when compared with those of a like age in 

 other parts of the country, and have been entirely removed by 

 denudation from many parts of the area, exposing the 

 original Pre-Cambrian floor. Peneplanation has taken place 

 during several successive periods which has reduced the 

 various geological elements to a common level and has spread 

 a covering mantle of sand, clay, and travertine limestone over 

 the whole which effectually hides the underlying rocks from 

 view. What makes the field work of the geologist still more 

 difficult is the absence of eroding streams, prominent land 

 forms, and railway cuttings, so that the only rock sections 

 available are in the sea cliffs or in well sinkings. 



Proterozoic. 



PRE-CAMBRIAN. 



Metamorphic and igneous rocks form the basement rocks 

 of the district (fig. 1). So far as observed they have a 

 north and south strike with a high angle of dip. The 

 exposure of these beds is, for the most part, inconspicuous, 



Fig. 1. 

 Section across Yorke Peninsula from Ardrossan to Port Victoria. 

 a, Pre-Cambrian Complex; b, Upper Cambrian Basal Grits ; 

 c, Upper Cambrian fossiliferous Limestone ; d, Outliers of Lower 

 Tertiary (Miocene) fossiliferous marine beds; c, Pleistocene 

 Mottled Clay and Sandstone and silicified Grits and Con- 

 glomerates ; /, mantle of soil and nodules of Travertine. — 

 Howchin's "Geology of South Australia." 



often occurring on cultivated land, and recognized by surface 

 stones, or proved, at shallow depths, by borings and well 

 sinkings, and it is certain that they cover a much greater 

 extent of country than is represented on the official Geological 

 Map of South Australia. In making the observations in the 

 field, here recorded, no attempt was made to determine the 

 extent of the Pre-Cambrian outcrops, so that the occurrences 

 noted below are the result of casual observations met with in 

 a general survey of the ground. 



1. Ardrossan. At a mile and a half distance from 

 Ardrossan, in a north-westerly direction, there is an exten- 

 sive field of Pre-Cambrian outcrops, and includes the old 

 Parara copper mine, which is on the northern side of the 



