244 



The glacial origin of these sandstones is still further 

 borne out by the microscopical structure of the stone, (plate 

 xlv.). In some cases, as in the main quarry (Collett's) of 

 the lower Finniss, the fragmental constituents are almost en- 

 tirely angular and often mere splinters; whilst in other in- 

 stances, as the Yankalilla sandstone, for example, there are 

 rounded grains intermixed with the angular. There is a 

 complete absence of interstitial cement, as ordinarily present 

 in fragmental rocks, and the stone has been made to cohere 

 by the interlocking of its angular particles and an infilling of 

 very finely triturated grains of the same mineral substance 

 as the larger fragments. This fine pasty material was pro- 

 bably of the nature of the "rock flour," which is characteristic 

 of glacial erosion, and which under the effects of very great 

 pressure has proved the cementing agent of the stone in ques- 

 tion. The material composing the sandstones is almost ex- 

 clusively quartz, but as casual constituents, some felspars, 

 aluminium silicates, and iron oxides have been observed in 

 the sections made. 



The sandstone, as developed in the neighbourhood of the 

 lower Finniss, makes a fairly good building stone, and has 

 been extensively used for this purpose. Several quarries 

 have been worked on either side of the river above the railway 

 bridge. The chief quarry now in operation is on Mr. Collett's 

 land, in Section 173, Nangkita, situated a little above the 

 district road bridge over the River Finniss. The quarry face 

 is about 30 ft. in height (plate xliii.), showing strong stone to 

 within a few feet of the top. The upper portion, as shown in 

 the photograph, is a softer stone, which, in weathering, has 

 brought into relief strongly-contorted bedding lines. The 

 main stone in the quarry exhibits no bedding planes, but there 

 are close joints which intersect the stone at high angles, 

 and, in places, are iron-stained. No quartz-veins occur, and 

 the rock resembles, in all respects, sandstones of the same age 

 and origin as developed at Yankalilla, Myponga, and other 

 places. As a building stone it was used in the construction 

 of the railway bridge across the River Finniss and many other 

 local structures, the railway station buildings at Strathalbyn, 

 the Bank of New South Wales in Adelaide, and the stone pillars 

 at the entrance gates of the Adelaide University (plate xliv.). 

 Its defect as a building stone is in its unequal hardness and 

 tendency to weather on exposure. Some of the masses of rock 

 that formed the outcrops of the bed were avoided by the work- 

 men as too hard for dressing, while, on the other hand, in the 

 case of some samples used in architecture, after thirty years 

 of exposure, they show a marked deterioration. When re- 

 building the pillars and coping-stones at the University 



