203 



but was a typical example of the coarse basal grits found 

 throughout the district as the lowest member of the Cambrian 

 System. 



This bore supplies important information on the geology 

 of the district which is not otherwise available. Not only 

 does it prove the existence of Cambrian beds in a locality 

 where there is no surface indications of their presence, but 

 it also supplies evidence in relation to (a) the position and 

 thickness of the (basal) grits; (b) the dolomites as ocupying 

 a position next to the basal grits in an ascending order of 

 occurrence ; (c) typical examples of purple slate interbedded 

 with the dolomites; (d) the thickness of the dolomitic rocks 

 to be something over 90 feet; none of which particulars 

 can be definitely obtained at the surface in any part of the 

 district. As the upper limits of the dolomite in the bore 

 section is shown to be a surface of erosion, it is most likely 

 that the original thickness of these beds exceeds the measure- 

 ments given in the section. 



Cainozoic. 



No beds of an age between the Upper Cambrian and 

 the Mid-Cainozoic, or Miocene, occur in that portion of Yorke 

 Peninsula to which these notes refer. The Permo-Carbon- 

 iferous glacial clays and erratics, which occur over wide areas 

 in the southern portions of the Peninsula, have not been 

 noted so far north as Ardrossan, while the geological form- 

 ations that are newer than the Upper Cambrian occur within 

 the district only as fragmentary and isolated outcrops that 

 are remnants of much more extensive deposits. 



MIOCENE. 



So far as the district under notice is concerned the older 

 fossiliferous beds of Cainozoic age are limited in their 

 occurrence to the eastern seaboard, and are found in two 

 parallel strips of different elevations ; one of these is situated 

 on the eastern edge of the central plateau, facing the sea, 

 and the other occurs at or near sea level. In the case of the 

 high-level deposits the material is limited to scattered 

 surface stones, found on cultivated land, at an elevation of 

 from 200 to 300 feet above sea level. These free stones are 

 in the form of a yellowish chert, and the fossils, which are 

 in the same material, are mainly in the form of casts. The 

 common fossil in these cherty fragments is TurriteJla 

 aldingae, which occurs in great numbers, and fixes the 

 geological horizon as that of the Turritella clays and cherts 

 of Aldinga and other places on both sides of Gulf St. Vincent, 

 which are now considered to be of Miocene Age. 



