374 PROCEEDINGS OF SECTION C. 



r—NOTE ON THE DISTRIBUTION OF THE GRAPTO- 



LITID^ IN THE ROCKS OF CASTLEMAINE. 



By T. S. HALL, M.A. 



The view formerly expressed by many authors who have dealt 

 with the Lower Silurian rocks in Victoria, that it was not pos- 

 sible to sub-divide the series either on lithological or on pala^onto- 

 logical grounds, is one that appears improbable if we consider the 

 great thickness that has been ascribed to the beds. It has been 

 stated that the Graptolites, which almost solely constitute the fauna 

 of the deposits, are all to be found throughout the series from 

 base to summit. An examination of the rocks of Castlemaine, 

 however, shows that this is not the case, but that certain forms are 

 characteristic of some localities, while others are found elsewhere. 

 At present I have many species that I am unable to determine 

 specifically, so that I must withhold a detailed discussion till a 

 later date. Of the identifiable fonns, however, there are some 

 which range throughout the series, while others afford a ready 

 means of distinguishing certain zones, and I have quite recently 

 been able to determine with certainty the order of succession. 



The texture of the rocks has frequently been described, ranging 

 as it does from coarse grits with grains ^in. in diameter down to 

 fine slates. Slaty cleavage is well developed all over the field, and 

 dips about 80° to the. westward. As in Bendigo, the anticlinal 

 folds follow in rapid succession, and I have traced thirteen in 

 two and a quarter miles. The strike is very constant, being about 

 N. 5° W., with an average dip of about 70°. The covmtry is very 

 rugged, though the hills are of no great height. 



The loAvest beds examined are well seen in Lost Gully, between 

 Chewton and Fryers, the faima being apparently identical with 

 that of the central area of Bendigo. This zone is characterised by 

 the abundance of Tetrayraptus fru/icoms, which ranges no higher 

 in the series. There are several other peculiar forms, notably 

 Goniograptus Thureaui and Thamnograptus typus. Other forms 

 with a wider range also occur, such as Didymoyraphis caduceus, 

 which is small and rare, but which increases in numbers and in 

 size as higher beds are reached. Associated with these are Tetru- 

 graptus quadribrachiatus, T. bryonaides, Dichoyraptus sp., and 

 Phylloyraptus typus, which have a somewhat extended range. 



These beds are seen in Wattle Gully to be overlain by a series 

 showing a somewhat diff"erent fauna. Tetrayraptus fruticosus has 

 disappeared, and the commonest form is Didymoyraptus bifdm. I 

 have found two other outcrops of this zone on ditt'erent anticlines to 

 the west, but cannot as yet directly connect it with the fossi- 

 liferous beds above it, as a considerable thickness of sandstones 

 and unfossiliferous slates, extending over several anticlines, 

 intervenes. 



