351 
broken by the elevated outlying spur forming the Eldon 
Range near Lake St. Clair. From Gad’s Hill in a south- 
easterly direction to the Table Mountain, a distance of not 
less than 90 miles, its similarly indented margin presents a 
still bolder character as it approaches and contrasts with the 
lower fertile plains and valleys of the Meander and South 
Esk, which seldom exceeds an altitude from 600 to 700 feet 
above sea level. At the great Northern and Southern water 
divide, in the neighbourhood of the Table Mountain, it 
suddenly recedes and contracts, forming a large bight in 
the direction of the Upper Derwent tributaries, notably 
the rivers Nive and Ouse, from which its level tends 
to fall, and its marginal boundaries, though frequently 
rising into high mountain ridges towards Mount Wellington, 
no longer maintains the uniform boldness of outline which 
characterises it in its northerly aspect. 
With the exception of Ben Lomond, which attains an 
altitude of 5,010 feet, the remaining isolated or ramifying 
ereenstone dividing ranges, distributed throughout the basin 
of the Tamar, Derwent, and Coal River, and along the broken 
or deeply indented coast line of the East, are tame in 
character when compared with the elevated far-extending 
tiers of the Great Central Plateau. 
Nearly everywhere along and against this plateau, and the 
greenstone crests of Ben Lomond, Mount Dromedary, Mount 
Nicholas, Eldon Range, Mount Gell, Grass Tree Hill, Consti- 
tution Hill, and most of the more elevated South-Eastern 
dividing ranges, the various members of the Carboniferous 
and Mesozoic rocks are seen to repose invariably almost in an 
horizontal position, or, at most, with a very slight dip towards 
or away from them. This general character is_ best 
appreciated by following the dark-grey color bands of the 
Upper Paleozoic and Mesozoic rocks as described in the 
sketch map referred to. 
In my opinion it would seem probable that the greater 
part of the greenstone rocks were erupted prior to the 
deposition even of the lower members of the Carboniferous 
mudstones, andat a time when, from secular causes, the older 
rocks of the South-Eastern and Central parts of the island, 
after long suberial exposure, were slowly being submerged 
below the level of the Upper Paleozoic sea. So far as 
existing evidences show, it seems to me that this depression 
must have occurred towards the close of the Devonian, or at the 
commencement of the Carboniferous, period. Strzelecki, who 
was the first observer who graphically described these rocks, 
thought that the main masses of greenstone forming the 
Western and such mountain chains as Mount Wellington and 
Ben Lomond, were erupted subsequent to the deposition of the 
