164 F. L. SfiUweU: 



angle on the opposite face. On the S.E. face the columns are in 

 part vertical, and o:radually pass into the inward sloping columns 

 on both sides. The quarry therefore marks the site of a pre- 

 older basaltic river valley. In a cliff section higher up the 

 stream the columnar structure is again evident. Here in the 

 upper part the columns are not so well defined, and in the lower 

 part some of the columns are very small and more or less 

 weathered. Still further up the stream the creek bed is formed 

 of pavements or columns in plan. These are mostly hexagonal 

 in outline, and frequently show irregular cracks, this being 

 the first stage of their disintegration. 



From the quarry a sample of the normal rock was taken, 

 sectioned and analysed. From this fresh rock all stages in 

 decomposition may be observed up to a soft, more or less iron- 

 stained, wackenitic clay. In one section below the quarry the 

 platy structure, and in part the spheroidal appearance, is de- 

 veloped, and at the bottom it is very soft and has the appearance 

 of a red earth, which in the hand specimen has somewhat the 

 appearance of a tuff. 



As regards geological relations, its precise age cannot be 

 determined in this area. It is clearly post silurian. Its rela- 

 tions Avith the tertiary quartzites will be discussed later. It 

 occurs mostly at a lower level than the newer basalt, and though 

 the two series come together in the northern part of the area, 

 the two are not visible together in one section. Its chemical 

 and petrographical characters show that it is distinct from the 

 newer basalt, and that it may be correlated with the older 

 basaltic series which has been shown to be in other parts 

 barwonian (5). 



Chemical Characters. 



The analysis of this rock shows by the low percentage of SiO.2^ 

 its very basic character. The alkalies, totalling approximately 

 5 per cent., are greater than the average of the basalts for 

 the SiOg percentage. This is impressed on one when working^ 

 out the norm under the American system of classification, which 

 brings an amount of nepheline into the composition of the rock. 

 Its position in the classification is — Class III., Selfamine ; 

 Order 5, Portugare ; Rang 3, Limburgase; Sub-Rang 4, Lim- 



