Identifier: transactionsproc4445phil (find matches)
Title: Transactions and proceedings and report of the Philosophical Society of Adelaide, South Australia
Year: 1878 (1870s)
Authors: Philosophical Society of Adelaide, South Australia
Subjects: Philosophical Society of Adelaide, South Australia Science
Publisher: Adelaide : The Society
Contributing Library: University of Illinois Urbana-Champaign
Digitizing Sponsor: University of Illinois Urbana-Champaign

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epressions caused by subsidence ofthe crust, consequent on the removal from below of such vastquantities of material as it is evident that has been erupted. Professor Howchin (see Ref. No. 4) supports the viewsof the previous writer on this point, adding:—The qua-quaversal dip points to one centre of ejectment, while thedepressed areas of the Blue Lake, the Leg of Mutton Lake,and the Valley Lake are undoubtedly sunken areas, the sub-sidence taking place late in the period of activity, or even afterthe volcano ceased to eject material. (b) Contour Map.—The writer has made repeated effortsto confirm this conclusion of Professor Howchin, but hisaccumulated observations of both dip and contour stronglysupport the conclusion of Woods that there was a very im-portant crater situated somewhere near the centre of thecollapsed area that now contains the Blue Lake. The evidencefor an undoubted crater near the foot of Tower Point (MountGambier proper) is equally clear. (19) Blue Lake. g2 188
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has therefore been prepared (see fig. 6). The hachured planof the Mount and lakes (10 ch.^l in.), prepared by H. 189 Jacob, of the South Australian Lands Department, in 1910,was made the basis of the contour map. Numerous traverseswere made around and across the area, wherever possible,taking two sets of aneroid observations by separate observers,and checking results at all intersections. The contour linesare plotted at 50-ft. intervals. It is not claimed that this is a correct contour map ofthe locality, but in all essential features it is sufficientlycorrect for the purposes for which it was prepared. It hasbeen found of great value in working out the reconstruction•of the cones prior to subsidence. (c) Reconstruction of the Cinder Cone*.—In attemptingthis reconstruction, two lines of supporting evidence are avail-able: (i.) the dip of the tuff beds where undisturbed ; (ii.) theexternal contours where unbroken by the collapse. It is therefore necessary to eliminate the areas dis

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