1. The Map.-Unless the geological work to be done merely consists in visiting already known ground and making detailed notes, or collecting specimens there, it is of the utmost consequence to obtain as good a map of the region as can be had. Not merely does the observer find the advantage of the topographical guide over the ground, but, as I shall point out in a succeeding chapter, he cannot, in many cases, satisfactorily work out the geological relations of the rocks unless he possesses a map on which to place, in their proper geographical position, the notes he makes at each locality. Hence if he cannot procure a map, or if he is at work in a country which has not yet been topographically surveyed, he may find himself compelled to make a map for himself with as near an approach to accuracy as the means at his command will admit.

2. The Hammer.-This is the chief instrument of the field-geologist. He ought at first to use it constantly, and seldom trust himself to name a rock until he has broken a fragment from it, and compared the fresh with the weathered surface. Most rocks yield so much to the action of the weather as to acquire a decomposed, crumbling crust, by which the true colour, texture, and composition of the rock itself may be entirely concealed. Two rocks, of which the outer crusts are similar, may

had entered it. The villagers were still standing at their doors, discussing the character of the new arrival, when we passed them. Of course we were naturally supposed to form a kind of rear-guard of the cavalcade; but we had the satisfaction of hearing one old woman remark to her neighbour, as we brushed past them, "Na, noo, arena' thae twa decent-looking chields to be play-acting blackguards ?"

differ greatly from each other in essential characters. Again, two rocks may assume a very different aspect externally, and yet may show an identity of composition on a freshly-fractured internal surface. The hammer, therefore, is required to detach this outer deceptive crust. If heavy enough to do this, it is sufficient for the purpose; any additional weight is unnecessary and burdensome. A hammer, of which the head weighs one pound or a few ounces more is quite massive enough for all the ordinary requirements of the field-geologist. When he proceeds to collect specimens he needs a hammer of two or three pounds, or even more, in weight, and a small, light chipping hammer, to trim the specimens and reduce them in bulk, without running a too frequent risk of shattering them to pieces.

Hardly any two geologists agree as to the best shape of hammer; much evidently depending upon the individual style in which each observer wields his tool. This (Fig. 1) is the form which, after long experience we have found in the Geological Survey to be on the whole the best. A hammer formed after this pattern combines, as may be observed, the uses both of a hammer and a chisel. With the broad, heavy, or square end, we can break cff a fragment large enough to show the internal grain of a rock. With the thin, wedge-shaped, or chisel-like end, we can split open shales, sandstones, schists, and other fissile rocks. This cutting or splitting edge should be at a right angle to the axis of the shaft. If placed upright or in the same line with the shaft, much of its efficiency is lost, especially in wedging off plates of shale or other rocks.

A hammer shaped as I recommend serves at times for

other than purely geological purposes. On steep grassy slopes, where the footing is precarious, and where there is no available hold for the hand, the wedge-like end of the hammer may be driven firmly into the turf, and the geologist may thereby let himself securely down or pull himself up.

The most generally convenient way of carrying the hammer is to have it in a leather sheath suspended from the waist-belt. The hammer hangs at the left side under the coat, the inside of which is kept from being cut or soiled by the protecting outer flap of the sheath. Some geologists prefer to carry the belt across the shoulders outside, and the hammer suspended at the back.

provide themselves with strong canvas coat-pockets and carry the hammer there.

3. The Lens. Even the most sharp-sighted observer is the better of the aid supplied to him by a good magnifying-glass. For field-work a pocket lens with two powers is usually sufficient. One glass should have a large field for showing the general texture of a rock, its component grains or crystals, and the manner of their arrangements; the other glass should be capable of making visible the fine striæ on a crystal, and the minuter ornament on the surface of a fish-scale or other fossil organism. Applied to the weathered crust of a rock, the lens often enables the observer to detect indications of composition and texture, which the fresh fracture of the rock does not reveal. It sometimes suffices to decide whether a puzzling fine-grained rock should be referred to the igneous or the aqueous series, and consequently how that rock is to be coloured on the map.

4. The Compass.-Any ordinary pocket compass will suffice for most of the requirements of the field-geologist. Should he need to take accurate bearings, however, a small portable azimuth compass will be found useful. This is the instrument employed in the Geological Survey. It is carried in a leather case or pocket hung from the waist-belt on the side of the body, opposite to the hammer. (Fig. 1.) The directions of the dip and strike of rocks, the trend of dislocations and dykes, the line of boundaries, escarpments, and other geological features are observed accurately, and noted on the spot at the time of observation, either on the map or in the notebook. A convenient instrument for light and rapid surveys, or reconnaisances, combines the compass and the

next instrument I have to describe—the clinometer. I

shall refer to it again.

5. The Clinometer, or dip-measurer, is employed to find the angle at which strata are placed to the horizon—an important observation in the investigation of the geological structure of a country, and one having frequently a special economic value, as, for instance, when it points out the depth to which a well or mine must be sunk. Various patterns have been proposed and used for this instrument. Formerly a spirit-level was commonly employed. But apart from the difficulty of rapid adjustment for the

requirements of the field, the spirit levels in the clinometers were apt to get broken. A much more portable and serviceable form of clinometer may be made by the geologist himself. It consists of two thin leaves of wood, each two inches broad and six inches long, neatly hinged together, so as to open out and form a foot rule when required. On the inside of one of these leaves a small brass pendulum is so fixed that when it swings freely and hangs vertically, it forms an angle of 90°, with the upper edge of the leaf to which it is attached. An arc, graduated to 90° on each side of the vertical, is drawn on the wood,