• Unaltered Lower Silurian Boclcs, 
35 
they are usually white, grey, brown, yellow, or reddish, occasion- 
ally mottled, and sometimes dark-grey or blue. Like the sand- 
stones, they are almost invariably dark-coloured below the water- 
level. 5 The cleavage and the stratification of the argillaceous 
layers are generally identical, but cleavage distinct from stratifica- 
tion is not uncommon. 
JS T o limestone bauds have yet been found among the rocks of the 
Lower Silurian series in the area west of Melbourne. 
The characteristic and most abundant fossils of these rocks are 
graptolites ( polyzoa ), on the evidence of which Professor McCoy 
was enabled to co-relato the Victorian Lower Silurian strata with 
those of Europe and America. 
In the commencement of the first decade of his Prodromus of 
the Paleontology of Victoria, Professor McCoy mentions that, 
shortly before coming to Victoria, he found in the slate-rocks of 
the old Roman gold-mines in Wales exactly the same species of 
graptolites as those which lie subsequently discovered to be the 
most common in the gold-field slates of this colony ; and that 
the Romans had in Wales obtained gold from quartz-veins 
traversing slates of exactly the same geological age as those of 
Victoria. , _ , . 
The series known as the Llandeilo flags and the Bala rocks in 
Wales are those to which our Lower Silurian rocks are shown on 
palaeontological evidence to he the equivalents. The various 
species of the family Graptolitidae which have been found in Vic- 
toria, and have been figured and described by Professor McCoy 
in his decades, are as follows : — 
rhyllograptns folium (His. sp.), var. it/ pus (Hall) ; JJiplo- 
qrapsus mucronatus (Hall sp.) ; D. pristis (His. sp.); D, 
rectanqularis (McCoy) ; D. bicornis (Hall) ; Didymograpsus 
fruticosus (Hall sp.) ; D. quadnbrachialus (Hall sp.) ; D. 
‘ bryonides (Hall sp.) ; D. octobrachiatus (Hall sp.) ;D. Logam 
(Hall) var. Australis (McCoy); D. extensus (Hall); I), caducens 
(Salter ); Diplograpsus palmcus (Barr sp.); Cladograpsus ramosus 
(Hall sp,); C. furcatus (Hall sp.); Didymograpsus gracilis ; D. 
Thtireaui (McCoy) ; D. Hcadi (Hall). The only forms other than 
graptolites, mentioned by Mr. A. R. C. Selwyn in bis essay, are 
Hymenocaris , Siphontreta (S. micula , McCoy), aud Lingula. 
The Silurian rocks occurring eastward of a line from the 
Macalister River in Gippsland to near Bonalla, have been pro- 
visionally referred to the Lower Silurian groups, partly on account 
of their lithological resemblance to those westward of Melbourne, 
and partly because of the discovery iu the slates at Deddick, 
near the New South Wales boundary line, of a graptolite 
(Diplograpsus rcctangularis , McCoy), and the identification at 
Gut tamur rli Creek, Snowy River, of Didymograpsus caducens 
and Diplograpsus fotiaceus in vertical slates capping the granite. 
