179 



The general appearance of the stratified tuffs, in section, 

 is quite like those of South-western Victoria and also the 

 better known tuffs of Lake Burrumbeet, though with much 

 less nodular basalt than the latter beds show. At Mount 

 Gambier huge ejected blocks of limestone, dolomite, and basalt 

 occur, with olivine bombs and blobs of ropy lava. Occasion- 

 ally, also, one may find flint nodules, waterworn quartz 

 pebbles, ( 10) and rare fragments of ancient rock (mica schist, 

 etc.). 



The foregoing features have been more carefully described 

 by others, but there is no record of the exact extent of the 

 ash deposits. With the able assistance of Mr. H. C. Hosking, 

 the writer investigated the limits of the ash deposits, with the 

 results shown in fig. 3. In this investigation the matter was 

 quite easy where road and rail cuttings, quarries, and sub- 

 sidences occurred ; elsewhere the fertility of the soil was noted 

 as evidence of the presence of ash, and this was corroborated 

 by the statements of the occupiers of the land, and by shallow 

 excavations. It is remarkable how light a layer of ash has 

 rendered the soil fertile as compared with that of the limestone 

 or sand-dune country, but there are also occasional areas of 

 good land beyond the limits of the ash deposits. 



On the outermost areas of the ash, the only evidence 

 consists of small, occasional, friable, light-brown nodules 

 that one soon becomes expert in recognizing. Such nodules 

 were also, later, found along the railway line, to the north- 

 west, as far as Mitchell Siding, but the deposit of ash must 

 have been here so slight that it has not been included in the 

 plan. Possibly one or two stiff "south-easterlies/' such as occa- 

 sionally occur here, would account for this light distribution to 

 the north-west. Howchin 1 ) states that the ash extended 

 seven miles in a north-easterly direction, but careful examin- 

 ation showed that this is not the case; the limit of the ash 

 in a north-easterly direction is a little over two miles. The 



(10) These waterworn pebbles may have been carried by 

 aborigines, whose flint flakes are abundant on certain parts of 

 the Mount. More likely, however, they were derived from the 

 occasional beds of sand and gravel that occur in the tertiary 

 beds; the records of the South Australian Department of Mines 

 show that sands and gravels were met in several bores in the 

 Hundred of Young, at depths between 100 and 150 ft. 



(11) "The Geography of South Australia," Howchin and 

 Gregory, 1909, p. 130. I am informed by Professor Howchin that 

 the above statement was made on the authority of the late 

 Professor Tate, who stated that the greater extension of ash in 

 a north-easterly direction could be explained from the prevalence 

 of south-westerly winds. 



