tory report, describing the nature of the soil, description of timber, &c., upon each section, and the facilities for making and repairing roads and bridges, and peculiar geological formations of the different districts. A collection of botanical and mineralogical specimens from all parts of the province will also contribute materially to the early development of its natural resources; and surveyors should not be deterred from giving their attention to this subject by ignorance of these sciences, as the specimens can be afterwards weeded and arranged, and afford invaluable statistical information.

At the head Survey Office a meteorological register * is of course supposed to be kept. It is also very desirable that each of the surveyors employed in any large district should be furnished with a good thermometer, rain-gauge, and a mountain-barometer, or aneroid, for the purpose of registering daily observations to be forwarded periodically to the general office for comparison with those obtained from different parts of the province, between which the difference of peculiarities of climate will be thus arrived at.

Surveyors working on a line of coast should be particular in noting all phenomena connected with the rise and fall of the tides ; and obtain soundings, laid down with reference to established and easily-recognised marks on shore, of all creeks and harbours, whenever this may be in their power. The depths and velocities of all rivers should also be noted at different points in their course, as well as the periods of floods, and their observed influence upon the volume of water in the river.

In laying out sections up narrow rocky ravines, or in situations where creeks or any other natural features present obstacles to the continuance of the methodical rectangular form, adopted as the standard figure, a deviation from this form becomes of course necessary, and the contents of some of the sections thus often unavoidably differ from the established average. Care should however be taken in such cases, to make the outline of these irregular figures as simple as the ground will admit of, both on account of the additional trouble and time lost in their survey, and the increased cost of subsequent fencing by the purchaser.

Attention has already been drawn in page 123 to the necessity of

* A simple form adapted for this is given at the end of the Astronomical Tables.

guarding against the monopoly of road or water frontage. The same sort of precaution is also required in marking out land in rich narrow valleys, or in spots valuable on account of minerals. As a general rule, from which no deviation whatever should be allowed, it may be laid down that no section should ever be permitted to enclose an undue proportion of land, unusually valuable from whatever cause, by extending its length in the direction in which that valuable portion of land runs; whether it be a rich agricultural valley, a mineral lode, a stream, or watercourse.

IB

As regards the actual marking out of the sections upon the ground, when the figure is of a square or rectangular form, the process is a very simple one; whether the true meridian, or the direct line of some main road, or a line forming any angle with the meridian that may be found better adapted to the local peculiarities of the district, be adopted as the guiding line of direction. A spot being fixed upon for the starting point, represented by A in the accompanying figure*, the normal line A B is carefully marked out by a good theodolite in the required direction; if intended to correspond, or to form any fixed angle with the meridian, this must be determined by one of the methods explained in the next chapter. The right angle B A C is then set off, which angle should be observed on both sides of A B (produced on purpose to D), and the

A

chain measurement along these lines A B and A C, and afterwards along the parallels to A C, may, if two parties are employed together, which can generally be managed under the charge of one efficient surveyor with an intelligent assistant, be carried on simultaneously; the points of junction at the angles of the blocks forming in some measure checks upon the accuracy of the work as it proceeds. The size of these sections, and the intervals between the parallel sectional roads, will depend of course upon local regula

* This figure represents rectangular sections of 80 acres, as laid out in South Australia, the length of which bore to their breadth the proportion of 2 to 1—occupation roads one mile apart, enclosing eight sections. They were, however, frequently laid out square, ac cording to the nature of the ground.

tions. The operation would evidently be simplified by running all the measured lines in the middle of these roads, leaving half their breadth to be afterwards set off on each side by the proprietors of the land, but the palpable objections to this are too serious to be compensated by the trifling saving thereby effected. In fact, the real boundaries of no one section are by this plan marked on the ground by the surveyor; and constant disputes and encroachments would be the consequence of adopting it.

It must be obvious to every practical surveyor, that it would be impossible for him to continue this mechanical system of marking a series of rectangular figures on the ground to any great extent, without being liable to constantly-increasing errors, which could not be guarded against by any degree of care in the operation, and of the amount of which he could never be aware, without establishing some check altogether independent of the chain measurement of the sections themselves; which is only to be accomplished by combining with it a triangulation of the country, more or less accurate, according to the nature of the survey. Whilst, then, this methodical division of the land is in progress, it is advisable, if anything like accuracy is required, and if the detached portions of settled country are to be laid down upon a general map, that the sites of the trigonometrical stations should be decided upon, and the stations themselves (however roughly they may be constructed) erected, in order that they may throughout be made use of as guides and checks upon the measurements. The triangulation indeed would be found of the greatest service, if carried on rather in advance of the detail, as in the survey of old countries. Any great accumulation of error could be then easily guarded against, by the angles observed at different parts of the chain survey, subtended by three or more of the trigonometrical stations; and in very many instances these stations could be actually measured up to, which should be done wherever practicable; by which means the marking out of the sections answers the same purpose that is obtained in ordinary surveys by the measurement of check lines, and traversing along the roads, by which the interior detail is mostly filled in. Angles of depression and elevation should also be taken to these trigonometrical points (whose altitudes are all obtained by the triangulation), from various

parts of the chain survey, the heights of which positions, above the level of the sea, are thus obtained with tolerable accuracy.

As to the mode of conducting this triangulation, all necessary instructions have already been given in the third chapter. The degree of accuracy with which the base is measured, and the angles observed, will depend evidently upon various contingencies; for instance the extent over which the triangulation is to be carried; the time and expense that can be bestowed upon it; the degree of minutia required in the maps, &c., &c. On the survey of South Australia the base was measured upon a nearly level plain very little elevated above the sea, with a standard chain; the operation being repeated several times, to obtain a more correct mean value : the angles were observed with a very excellent 7-inch theodolite; and the result was found sufficiently accurate for the purpose of connecting all the detached blocks of surveyed land, and laying down the work to the scale of 2 inches to 1 mile.

In addition to the above use of the triangulation, it is found, in the survey of a wild country, peculiarly serviceable in enabling the Government to define, with the aid of marked natural features, the boundaries of the extensive tracts of land leased to different individuals for pasturage, until, with the increase of population and civilization, more convenient and better-defined demarcations are substituted. Some of the principal natural landmarks of a country also, such as chains of mountains and rivers, traverse the wildest parts of the land, where chain surveying would never penetrate. Many of these landmarks are made the boundaries of counties, and other internal territorial divisions; and their positions in different parts of their course are often only to be determined by reference to the trigonometrical stations, which likewise serve as guides for ascertaining and laying down upon paper the directions of roads through extensive, barren, and uninhabited tracts of country.

Most of the foregoing remarks have been made under the supposition that a number of detached surveying parties are distributed over different parts of the country, all working under the directions of, and reporting to, a central Survey Establishment. As the population becomes distributed over a wider extent, and applications are constantly made for the survey of small, irregular

K

blocks of land, to complete and consolidate properties, some alterations will be required in the method of carrying on the measurement of land, to meet these new demands*. It could evidently be only by an increased expenditure of time and money that surveying parties could be kept constantly moving from one distant spot to another, to lay out perhaps, only a very limited number of acres at each; and the division of the country into Districts, for the purposes of the survey, becomes almost imperative. Copies of the plans of sections open for selection, and other information of a similar character, would be thus placed more within reach of distant settlers, and their wants could more readily and rapidly be met without augmented expense.

Portions of the work might also at this advanced stage of progress be filled in by contract, subject to careful and rigid examination; the triangulation, and the previous chain measurement connected with it, affording sufficient checks for this purpose; without which, surveying by contract should be most carefully avoided, especially in new communities where but little competition can be expected, and where it would be unreasonable to expect to find competent surveyors distributed over the remote parts of the colony.

The rate of progress and cost per acre of a sectional survey such as has been described, must vary considerably, according to the nature of the country, the prices of labour and provisions, and the minuteness of the divisions. If the size of the sections is small, 80 or 100 acres for instance, the number of lineal miles to be measured is of course very much greater in proportion than would be the case with blocks of a larger area, and the progress must bear an inverse ratio to the increased expense. The facility of transport is another item that materially influences both these questions, as also the system of marking out patches of land in whatever locality they may be applied for, instead of carrying

* These subsequent wants and demands do not affect the first stage of the survey in a new country; it is only as it becomes gradually settled that they are felt. The first survey evidently cannot be a complete one, unless it could embrace every acre of land that might by possibility be required; it is constantly demanding extension in every direction, therefore the more imperatively necessary is it, that the first land surveyed and laid down on the maps should be based upon a triangulation sufficiently accurate to allow of this extension, without the certainty of accumulating error.