494 flarrison—On the Geology of Hobart Town. 
the beds, a lateral pressure may also have led to a phenomenon 
somewhat analogous to what talees place when the pieces of ice in 
a large floe begin to pack one upon the other. Hence the apparent 
anomaly just alluded to. 
From whatever cause these secondary fissures arose, they do not 
seem to have been filled up with the basalt which they now contain 
contemporaneously with their formation. Still, the time elapsing 
between the fracturing and eruptive forces may have been extremely 
short; what is meant being, simply, that the fissures referred to do 
not owe their origin to the protrusion of the basaltic dykes by which 
they are now completely occupied. 
Of the rocks met with in the district, the lowest is of an extremely 
fossiliferous character, and is called by the colonists Mountain or 
Carboniferous Limestone (?). It appears to be divided into two 
distinct beds. ‘The lower contains much lime and a profusion of 
bivalves (Spirifera, Pectinide, and Producta), and the upper being 
more arenaceous, and inclosing a large quantity of corals (Lenestella 
and Stenopora). 
On the sides of Mount Wellington are a number.of erratic blocks, 
containing a larger number of spiral univalves. Such blocks are of 
great hardness, and seem in some instances to be nearly made up of 
arenaceous particles; but it must not be supposed that this variety 
in organisms and texture indicates a formation upon a horizon dif- 
ferent from that of the adjacent limestone. 
Above these beds is a dense compact stratum, locally known as 
‘mud’ or ‘clay stone.’ According to Mr. Selwyn, it is upwards of 
400 feet in thickness. In a few places impressions of shells are dis- 
coverable ; but generally fossils are of rare occurrence. Scattered 
here and there throughout the mass are numerous pieces of quartz 
and other rocks. 
It was probably the prevalence of vast quantities of turbid water, 
originating this deposit, which so completely destroyed the immense 
growth of corals characteristic of the upper beds of limestone. 
Immediately over the ‘clay-rock’ is superimposed a great thick- 
ness of sandstone. This stratum, also, is especially barren of any 
remains of animal life; but sandstone generally forms a bad matrix 
for the preservation of fossils. 
Interstratified with the upper portion of the sandstone beds are 
layers of shale bearing impressions of ‘ fern-leaves’ and ‘calamites,’ 
together with one or two layers of coal, changed, for the most part, 
into anthracite. The absence of Sigillaria, Stigmaria,* Lepidoden- 
dron, and other genera characteristic of the English Coal-measures, 
would seem to suggest that the coal of Tasmania, like that of 
Victoria, is not of the true Carboniferous period. 
What may, in some measure, go to confirm the opinion so hazarded, 
is the discovery in the sandstone of a bone, said by Professor Owen 
to be the ‘femur of a Labyrinthodon,’—a reptile, if I mistake not, 
generally associated with rocks of the Triassic age. 
A Hobart Town geologist, Mr. Morton Alport, speaking to me 
* See Note at the end. 
