The course of the Hawkesbury above Emu plains presents a singular feature in forcing its way through a very steep-sided ravine, and thus cutting off a portion of the mountain mass after its channel has previously bordered on the lower country of Cumberland where no such obstruction is opposed to its waters, which might there pursue a more direct course to the sea. The river takes this remarkable turn near the junction of the Nepean, and there we find in the bed of the stream (at Cox's Basin) a dark-coloured trap-rock, apparently containing steatitic matter, and doubtless connected with one of the disturbing operations to which this fractured country has been exposed. Beyond the ferry the road crosses Emu plains, a level tract, here about a mile in width, and intervening between the river and the base of the mountains. This flat consists chiefly of gravel--composed of large pebbles, for the greater part quartzose; and in sinking a well, a bed of them was found in which many were nearly spherical. TOWNSHIP. A township has been marked out at the ascent of the new road, the question as to the most eligible situation for a town on Emu plains having led to the construction of the new pass. The growth of towns depends very much on the direction of great roads, and must be more certain, and the allotments consequently more valuable, when the most eligible line of thoroughfare is ascertained and opened, in the first instance. Such works of public convenience should precede, as much as possible, the progress of colonisation. The plan at least should be well considered before the capital, or the labour, which is the same thing, is applied. Buildings and other improvements can then be commenced with greatest certainty of permanent value. GENERAL ARRANGEMENT OF TOWNS AND VILLAGES. "Les depenses utiles sont economie," said Guibert, but in new countries the economy will much depend on the permanent utility of works for which, in most cases, the necessity should be foreseen. With the example of so many old countries for our guidance, obstructions to the spread of population in a new one should be removed, according to plans of general arrangement, keeping in view the best distribution of towns with respect to local advantages, and the best sites for all public buildings requisite for the towns still in embryo. The most advantageous general lines of direction should be ascertained for the roads--that the public means may be applied with certainty to their substantial improvement by removing obstructions and building bridges. On good roads there is greater inducement to individuals to erect inns; and in well arranged streets to build good houses--than where uncertainty as to the permanent direction of the one, or irregularity in the plan or line of the other, discourage all such undertakings.