38 
Geology and Physical Geography : 
polished, the limestone base is nearly black, while the fossil 
markings are white, giving the stone a somewhat ornamental 
appearance. 
Among some very imperfect fossils collected from one of these 
patches at Cooper’s Creek, near the Thomson River copper-mine. 
Professor McCoy was enabled to identify Favosites Goldfussi with 
traces of a lamelliferous coral closely allied to Diplophyllum 
ccespitosum, small branching forms allied to Trematopora astiolata 
and Cladopora fibrosa , and one B eyrie hia allied to B. lata , with 
crinoid stems of the Actinocrinus type. 
From another patch on the south side of the Thomson River, 
between Walhalla and Toongabbie, were obtained numerous 
crinoid stoms of the Actinocrinus type, some traces of Gasteropoda 
apparently of the genus Acroculia, but too imperfect for determi- 
nation, and a fragment of Bellcrophon. 
From a third patch on t ho banks of the Deep Creek, a branch 
of the Thomson, were obtained only indeterminable fragments of 
crinoid steins and the coral allied to Trematopora astiolata found 
in the Cooper’s Creek limestone. 
This imperfect pala3ontological evidence was, in Professor 
McCoy’s opinion, closely indicative of Upper Silurian, though at 
one time there appeared grounds for believing that the various 
limestone patches referred to — clearly identical with one another 
in geological position — might be Devonian, as they appear at first 
sight to fill deep hollows or pockets in the ordinary Silurian 
rocks, and to be the vestiges of what were once more extensively 
developed beds of more recent date. On further examination, 
however, it was found that they are in reality portions of lenticular 
shaped beds of limestone, of limited extent, intercalated with the 
ordinary Upper Silurian rocks. When the Upper Silurian rocks 
were in process of deposition as sediments, isolated colonies of 
various forms of marine life appear to have occupied portions of 
the sea-bed ; these extracted lime from the sea water, and by their 
action beds of limestone were formed over limited areas, while 
around them the ordinary deposits of silt, &c., were being 
accumulated. They were subsequently covered, indurated, and 
folded with the rest of the Silurian rocks, and here and there have 
been laid bare by denudation, so that they present the appearance 
of wedge-shaped vertical masses of limestone fit ting into cor- 
responding “ pockets ” in the slates. 
In one well-marked instance, near the Thomson River, between 
Toongabbie and Walhalla, a quarry has been opened in the 
encrinital limestone, or marble, on the brow of a steep hill ; down- 
ward the limestone disappears, and nothing but slates and shales 
can he seen along the face of exposed rock below the quarry. In 
the bed of the creek at the bottom of the hill, and in the same 
line of strike with the large limestone mass above, is a small 
