62 J. T. J Litii07t : 



some doubt has arisen as to its correctness. On a recent visifc 

 to iVlelbourne, the writer intended to visit the ground, but unfor- 

 tunately time did not permit. The question is, however, now 

 brougtit forward as a suggestion for further investigation. 



Mt. Cooper is a rather prominent landmark, rising to a fair 

 height above the Newer Basalt of the Darebin Creek valley, and hav- 

 ing steep northern and western faces. There is a large patch of 

 Kainozoic sediments (most of which have been converted into 

 quartzite), which rest on the Silurian rocks of the district, and 

 underlie the basalt. This quartzite outcrops freely on the northern, 

 western and southern slopes of the hill, and is found right in the 

 bed of the Darebin Creek to the west.i These silicified gravels and 

 grits are no doubt part of, and originally continuous with, the 

 Kainozoic sediments of Preston and Greensborough, to which refer- 

 ence has already been made. 



The basalt cap is at the northern end of the hill, and is probably 

 from 40 to 50 feet thick at the highest point. This basalt, when 

 examinued in aifu, is, so far as observed, dense and non-vesicular. 

 Its boundaries are clearly shown on the northern, southern and 

 western sides, where the quartzite already referred to crops out 

 fi-om beneath the basalt. To the west, in the valley of the Darebin 

 Creek, is the low-lying lava flow, the typical Newer Basalt of the 

 district, from which the high basaltic cap of Mt. Cooper is separated 

 by the quartzite. 



According to the Survey map, the basalt of the hill is continuous 

 with the lower basalt at its north-eastern end, and on this ground 

 no doubt, the higher basalt has been mapped as Newer Basalt, and 

 the hill consequently regarded as a volcanic vent. An important 

 (piestion therefore is whether the two basalts are actually connected 

 oi- not. 



At first siglit there appears to be no doubt that such a connection 

 exists as although an actual outcrop cannot be continuously traced, 

 the heavy black soil resulting from the decomposition of basalt 

 forms an unbroken line on the north-eastern face. In addition, near 

 the top of the Mount, and on the same face, numerous pieces of 

 very vesicular basalt of low specific gravity, Avhich might for con- 

 venience be called basaltic pumice, occur. This is somewhat sugges- 

 tive of a vent in the neighbourhood. There is also a low hill be- 

 tween Mt. Cooper and the main road to the east, rising above the 

 level of tVie low-lving basalt. This hill has highly vesicular basalt, 

 which is apparently connected with the lower flow. 



1 This .shows that ,at this locality tho K.iinozdic sedinu-iits were deiiositi<l on an iiiiuven 

 Mirfaco, or thiit they h;ive l>tcii let down l.y fiiiiltiny. 



