418 PROCEEDINGS OF SECTION C. 



solution is continued to saturation or dryness, as in the case of the 

 recent oolitic deposits referred to. If this be so, then the extensive 

 development of the oolitic structure in the Upper Cambrian beds of 

 this State would suggest that they were formed (at least in part) under 

 practically subserial conditions. Again, the coarsely concretionary lime- 

 stones bear an exact resemblance (differences of age being taken into 

 account) with our concretionary travertine limestones, which form 

 over the surface of calcareous soils in all the drier parts of Australia. 

 The concretionary, or nodular, Cambrian limestones break up readily 

 into rounded fragments in a similar manner to this nodular travertine 

 limestone of recent origin, and can best be explained, I think, when 

 referred to a similar origin. The finely laminated limestones in the 

 Cambrian series also bear a likeness to such travertines as are laid down 

 from slow-moving surface waters when charged with calcium carbonate 

 in solution in an arid climate. A microscopical examination of these 

 interesting limestones is in progress, which may possibly throw further 

 light on the nature of their origin. The whole of these facts taken 

 together make, I think, a strong presumption that at certain intervals 

 of the Cambrian Period in these latitudes arid, if not desert, conditions 

 prevailed, and that much of the material laid down in Cambrian deposits 

 was of terrestrial origin. 



The second point referred to as of special interest in the Flinders 

 series is the great volcanic field which was developed in Post-Cambrian 

 time, chiefly at or near Blinman, forming the central part of the elevated 

 dome. The country is riddled with basic dykes, which have a general 

 east and west direction, but are not continuous for long distances, and 

 are sometimes circular, which suggests that some of them may be old 

 volcanic necks. Two considerations seem to point in the direction that 

 the volcanic activity belonged to a late stage of the elevation of the 

 dome, and that the dykes were formed at no great depth from the present 

 surface, viz., the lava of the supposed necks is often vesicular in 

 structure ; and, secondly, whilst the slate and other rocks which have 

 been penetrated and reduced to breccia by the intrusive dykes show 

 contact effects, they have undergone no secondary metamorphic 

 changes in the mass, which might be expected to occur had they been 

 brecciated at considerable depths. 



As these observations have only recently been made, time has not 

 permitted a petrological examination of the intrusive rocks. These 

 dykes often run parallel with or intersect the dolomitic limestones of 

 the district, and it is in the zone of junction of the limestones with the 

 intrusive rock that the mineral deposits of the neighborhood chiefly 

 occur. 



The lowest beds of this section comprise slates, flags, and dolo- 

 mites, but do not expose the base of the purple slates series. In other 

 parts of the Flinders Ranges the lower members — as low as the glacial 

 till beds — are at the surface. These have a general strike from south- 

 west to north-east. 



The Cambrians thin out on the western side against the Pre- 

 Cambrian massif of the western plateaux, as in the case of the Tent 



