Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/322

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But however defective and however misplaced in point of distance many of the most remarkable boundaries can scarcely fail of being, it is sufficiently accurate in the general features for all geological purposes. The sections are necessarily general, and are given not as actual sections of any particular points, but as illustrative of the relative superpositions of the rocks.

The course of the Tilt may therefore be considered as bounded on one side by the outer edge of the granite mass of the Grampians, and on the other by the primary rocks which follow and are superimposed on it. These rocks consist of an alternation of limestone, schist, and quartz rock.

The bed of the river is cut upon the line of contact of these two separate classes of rock, lying upon the surface of the granite, and against the elevated edges of the stratified rocks.

Its action has in various instances exposed the junction of the granite with the stratified rocks, and these exposed parts are the confused mixtures in the bed of the river which have already been described

Although the river follows this line of junction in a general view, it does not follow it so accurately as always to keep the granite on its right bank, and the stratified rocks on its left. For this reason the stratified rocks are sometimes seen crossing to the right bank, and even ascending high up the right side of the hill. The granite also crosses to the left in a few cases, but as it dips under the stratified rocks it is not found in the hill.

The Sections which are given illustrate this variation and explain its cause.

The apparent alternation of the granite with the stratified rocks is also explained by attending to this arrangement.

The granite masses which extend beyond the general surface of