256 
epoch. The chief facts are that in the neighbourhood of 
Ardrossan a lower series of metamorphic slates and lime- 
stones is covered unconformably by fossiliferous limestones of 
the Lower Silurian epoch ; and, though the lower series, un- 
derlying the fossiliferous limestones and associated strata 
about Ardrossan, cannot be brought into direct relationship 
with the fundamental rocks on this side of St. Vincent Gulf, 
yet their mineral character and sequence place them in 
accord; and the same may be said of the rocks constituting 
the high lands on Eyre's Peninsula. In this quotation 
Tate co-ordinates the Mount Lofty beds with the basal beds 
at Ardrossan, which at the time he classed as pre-Silurian, 
and later as Archean; the grounds of their assumed identity 
being based chiefly on their supposed lithological resemblance. 
Tate also differed from Burr, Selwyn, and Ulrich in his 
view of the order of succession shown by the Mount Lofty 
beds. The earlier observers mentioned believed that the 
beds passed from newer to older in their eastward extension, 
whilst Tate interpreted them in the reverse order. In the 
address already quoted he says: —* "The strata composing the 
principal range of South Australia have a general dip to the 
south-east, and show a succession of clay slate, with quartzite 
bands, crystalline limestones, mica slate, and other de- 
cidedly metamorphic rocks, and granite. It is remarkable 
that the appareutly less metamorphosed strata occupy the 
lowest position, whilst the uppermost stratum is gneiss, un- 
less we regard the granite, which follows next, in the light 
of the extreme of alteration of which the gneiss is an earlier 
phase. That the highly metamorphic rocks do not form the 
axis of the Adelaide chain is beyond dispute, and in various 
traverses across the strike of the strata of our hills I have 
failed to detect faults or inversion, which would account for 
their exceptional position, whilst, on the contrary, the suc- 
cessional arrangement is sufficiently clear to leave little room 
for question." 
The above assumption, that the Mount Lofty Ranges, 
throughout their entire width, represent a single monoclinal 
fold, would involve an enormous thickness of beds. This 
view is maintained by the late Professor Tate, who quotes 
Selwyn's estimate that the beds between Normanville and 
Encounter Bay are nearly 30,000 ft. in thickness, and adds, 
“There cannot be a doubt that the thickness of these funda- 
mental rocks is much greater in those portions of the cen- 
tral chain, near Adelaide, than in the Cape Jervis promon- 
tory." He also quotes Mr. Scoular, who believed that the 
beds exposed in the South Para River had a thickness of 
ы Op. cit., p xliii. 
