68 Notes on the Geology of the Country around Goulburn. 



region of stratified granite or gneiss, which blends comforinably 

 upwards into schist ; here these rocks are overspread by a thick 

 capping of basalt. The basalt lasts for four or five miles, until 

 we recross the Wollondilly, near the Black Springs : a little 

 beyond this we lose the granite, and pass over a rough country 

 of slate and quartzite, but on approaching the dividing range we 

 find every hill top above a certain level capped with basalt ; and, 

 on finally reaching the greatest elevation, the whole country for 

 some miles around becomes eutirely covered with this igneous 

 material. 



This section shows the main geological features to be met with 

 in the county of Argyle. A second section, taken along the 

 line indicated on the map from a part of the dividing range west 

 of Collector to Lake Wologororig, and thence east to the 

 Shoalhaven shows, on its eastern extremity, the only feature of 

 importance which the first fails to include. This formerly omitted 

 feature consists of an outlying patch of the white conglomerate 

 belonging to the coal formation. As it occurs on the top of the 

 loftiest spurs on the right bank of the Shoalhaven it is properly 

 in county St. Vincent ; but it is included in this section for the 

 sake of showing its relation to the rocks of the county now 

 under consideration. The rest of the coloured section explains 

 itself. These two sections also show the elevation of the country 

 between the Wollondilly and Shoalhaven ; the remarkable 

 difference in the heights of those two river courses though so 

 near together, suggests the idea of main stream and tributary 

 rather than two independent river systems. Section No. 3 shows 

 the same contrast in the elevation of these contiguous channels ; 

 it is drawn from Gibraltar Rock southwards over a barren tract 

 of quartz porphyry as far as Marulan ; it then takes a bend to 

 S.E. to the junction of Bungonia or Calne Creek with the 

 Shoalhaven. This part of the country has been minutely 

 described by Mr. Clarke in his " Eesearches in the Southern 

 G old-Fields." 



Section No. 4 shows the structure of the country in the 

 direction corresponding; with the respective line upon the map. 



FOSSILS AND AGE. 



The age of the rocks may next claim investigation. The 

 transition of the granite on the Shoalhaven and Wollondilly into 

 the ordinary overlying strata is so strikingly evident, that I am 

 inclined to assign to these granites and their associated deposits 

 the same age. With regard to the particular age of the stratified 

 rocks fossil evidence is rather scanty, but from the kind assistance 

 which I have received from Mr. Clarke, I am enabled to offer 

 some remarks upon the few fossil specimens collected. I have 

 already alluded to the shells near Atrypa hemisphosrica, and 

 Spirifer pliactellus, found near Bungonia ; also, the other genera 



