196 



met by Government borings in the district which will be 

 described below. 



On the evidences obtained the limestones may be classed 

 under three divisions : — 



Upper — Dark-coloured, impure, pteropod-trilobite 



limestones. 

 Middle — White, yellow, and pinkish marbles 

 (Archaeocyathine marbles in part). 



Lowe?' — White and yellow granular-crystalline 

 Dolomites. 



The following are brief descriptions of all the exposures 

 of these beds which have come under my notice in the 

 neighbourhood : — 



UPPER AND MIDDLE (FOSSILIFEROUs) BEDS. 



1. Horse Gully. The most complete and interesting 

 section of the Cambrian limestones within the district occurs 

 at Horse (or Pavey) Gully, situated a little to the southward 

 of Parara Head Station and 3 miles southward of 

 Ardrossan. It forms the deepest eroded valley in the dis- 

 trict, with sloping sides and rocky terraces, that have a 

 maximum height of about 200 feet. The gully, in its exit 

 to the sea and lower portions, possesses clay banks, and 

 these continue in an upstream direction for about a quarter 

 of a mile to the westward of the main road, beyond which 

 the limestones make a sudden appearance in the floor and 

 sides of the valley. The gully intersects the limestones, in 

 an east and west direction, for about a mile and a half. The 

 beds roll by slight synclinal and anticlinal curves, at an 

 average angle of about 12°, which increases somewhat as 

 the beds pass eastwards before their disappearance below sea- 

 level. The stronger beds make small scarp-faces on the sides 

 of the valley, and in the case of one sucji prominent outcrop 

 that encircles an isolated hill near its summit, there is a 

 striking resemblance to a monk's tonsure. This feature 

 illustrates the approximate horizon tality of the beds. 



The best section occurs soon after the appearance of the 

 limestones in the lower part of the valley, where an anticline 

 brings into view a great thickness of beds, and the following 

 order can be observed on the northern side of the valley: — 



Thickness 

 in feet. 

 (a) At the summit is a capping of Tertiary chert, 

 crowded with the casts of Turrit ella aldingae, 

 forming a hill that is conspicuous from its 

 conical form and growth of sheaoaks 50 



