Torrents sometimes form lakes and pools by the accumulation of their deposits obstructing further egress.

Torrents are occasioned either by the rapid thawing of snow in the mountains, or by very heavy or periodical rains. At what time of the year does this melting of the snow take place or do these rains fall? What winds bring the latter; how long, generally, do the rains continue to fall, or does the snow continue thawing?

Torrents occasionally cause the most dreadful ravages, and, consequently, in well-peopled and civilized countries, various means have been devised and practised with greater or less success to secure the country from their devastations; it is, therefore, of the greatest importance to examine the several methods adopted, the principles on which these methods are founded, and the degree of success which attends them.

The imprudent denudating of the hills has frequently created torrents where none before existed, and the covering the heights with trees has, sometimes, greatly contributed to diminish the velocity of torrents. It is also very necessary to examine the nature of the débris brought down by the torrents, particularly in exploring a new country, as these often lead to the most important discovery of mineral

treasures.

RIVERS.-Name.-Is the name the same from the source to the mouth of the river or different in different parts? Have the several sources, the anastamosing and deltic branches, when such exist, the same or different names? Specify the points at which the names change, the extent, direction, and nature of each separately named part, in all the detail indicated below, proceeding from the source towards the mouth, or vice versa, stating in which order.

What names has the river formerly borne? When, why, and by whom changed? Does it still bear different names, and if so, what are these names, and by whom are they respectively used ?

Have the present or former names any relation to the quality or nature of the river, the vegetation on its banks, or other natural circumstance, or to any traditions, superstitions, or historical facts? If so, state the precise signification of the name.

It sometimes happens that the part of a river immediately below its junction with some other river, is dif

ferently named by the inhabitants on the opposite banks,

thus, the inhabitants at A, accustomed to regard a d as the river, give the same name to the part c d as to the part a c, and say that be falls into a d. The inhabitants of B, on the contrary, consider b d as the river, of which they look upon a c as an affluent. Now, should these waters at the point d disembogue into some other river, which we shall call x, it would be said by different travellers, according as they had their information from the side A, or the side B, that the b c river falls into the ad, or that it falls into the x.

On the spot this may be of little consequence, but in travellers' accounts of countries little known, this circumstance should always be enquired into to avoid error. The above is exemplified in the case of the rivers Bug and Narew in Poland.

Origin.-Does the river derive its origin from one or several sources or springs, or from a lake or a marsh? What is its height above the level of its mouth? See SPRINGS, LAKES, MARSHES.

Course. Is the general course straight, (a), serpentine, (b), meandering, (c), or winding, (d), or any compounds of these, in toto or in part.*

Thus the Vermejo and the Magdalena may be called

The figures are supposed to represent, not any portions of rivers, but their whole course from origin to recipient.

straight-serpentine, the Nile meandro-serpentine, the Orinoco winding, &c.

As it may perhaps be objected by some, that the forms of rivers are not sufficiently precise to admit of this classification, I will observe that they are more precise and determined than the forms of clouds, which have, nevertheless, been classed and named, and the classification generally adopted.

What is the general direction, (true or magnetic being stated,) in one line or in several, according as the river winds more or less, omitting always the minor curves and sinuosities?

The length of the several lines individually and in toto, and the length in following the bends, stating always whether these lengths are presumed, asserted, or actually estimated, and, in the latter case, by what means.

Very extraordinary bends in meandering rivers, as those in some parts of the Missouri, should be particularly noticed, stating the circuit the bend takes and the direct distance across the isthmus.

Does the river in its course run through the middle of the valley, or does it cling in preference to the base of the heights on either side, and, if so, which side, or does it change sides in different places? Does the river run through a longitudinal valley, or does it cross one or more longitudinal valleys and their dividing ridges, and, if so, under what angle, and what are the appearances where the ridges are intersected by the stream? Is there at this point an anticlinal dip on both sides, or not; are the strata horizontal, or vertical, or synclinal; what is the nature of the rocks, are they the same on both sides or different; are the surfaces smooth and water-worn, or fragmented and confusedly heaped as if by sudden falling in of a cavern, or by explosion from below, or forcible rending?

Recipient-Is the recipient some other river, or a marsh, or a lake, or the sea? In either case, what is its name and the place of junction, which latter may be either approximately or absolutely determined in different ways, as, astronomically, or by actual admeasurement from some known point, as a town, a fortress, a castle, a ruin, a remarkable rock, either on the river itself or on its recipient, or by distance and bearing from some striking or well known object away from either.

Mouth. If the river empty itself into a recipient by

two or more mouths, it forms a Delta (which see); if by one mouth only, observe its width, and depth, and the angle formed by the affluent and recipient. Has the mouth of the river undergone, or is it still undergoing any notable change; and of what kind. Have the former changes been sudden or gradual, and are they rendered evident by, or are they merely presumable from, the nature and present configuration of the soil about the river's mouth, or is there any historical or traditionary evidence of such change?

Is the apparent breadth, mass of water and rapidity such as might be expected from the length of course and general size of the river, or is it greater or less? In either of these latter cases, state the ascertained or probable reason of such anomaly. In the first case it may be owing to a subterranean affluent or springs, in the latter, the diminution may be occasioned by a subterranean drain or by infiltration through the soil, or extraordinary evaporation.

Does the river form a bar, or shoal, or islands at its mouth, if so, what is the extent, direction and nature of such deposits; how far do they obstruct or endanger navigation; or, in the case of the river emptying itself into the sea or a large lake, how far do these objects contribute to the security of anchorage within them? Are the shoals at all times covered, and with what depth of water at different seasons, or tides, if such exist; or, if periodically uncovered, at what times of the year? Are the deposits permanent as to place or are they liable to shift? Are all or any of these undergoing increase of size, or diminution?

When rivers on approaching the coast, as is frequently the case, turn suddenly round so as to follow a course parallel to the sea before emptying finally into it, observe the direction of this bend in reference to the prevailing winds and currents of the sea or the ocean at that spot.

A Delta.-Deltas are Fluviatile when formed at the entrance of one river into another; Lacustrine, when at the embouchure if a river into a lake, and Maritime when the river falls into the sea. The original cause of a Delta is sometimes a natural obstacle, which splits the stream into two branches, but it more commonly results from a bank deposited by the river itself: Thus the soil of deltas, generally, is alluvial and, as such, fertile, unless the river brings down nothing but pure sand. The alluvial soil is sometimes confined within the two external or deltic branches of the river, but more frequently it extends beyond these.

Within the deltic branches there are frequently many other diverging and anastamosing branches, which for distinction's sake may be called Ana-deltic, and which cut up the delta into a greater or less number of deltic islands.*

Besides such observations as may be dictated by the forgoing remarks, it is necessary to notice the direction and length of each of the deltic branches from the point of divergance, and the angle they make, together with the distance from the mouth of the one to that of the other, or the base of the delta; the number of channels exclusive of the two outer ones; the number and particular names, together with the breadth and depth, of those that are navigable, and the preference that is, or should be, given to any of these, and why? What is the superficial extent of the space contained within the deltic branches, and the nature of the soil, as sandy, swampy, or fertile; and if the latter, what is the nature of the vegetation? If subject to inundation, at what time of the year and for how long; to what height does the water generally cover the land, and what thickness of deposit is annually accumulated? Are any of the channels subject to change, and, should the delta increase in size, to what extent and in what direction?

Confluence of two rivers. Is the recipient stream increased in width, in depth, or in velocity only, after receiving the waters of the affluent, or in any two, or all three, of these ways? stating the increase of width, depth, or velocity. It frequently happens that the waters of the two meeting streams are of different colour, or that the one is clear and the other turbid. In either of these cases it may be noticed how far below the point of junction the waters flow without commingling. Does the velocity of either river in times of flood impede the progress of the other so as to cause in either a rising of the waters, a back-current, or an inundation? Does this happen annually, and what is the extent of the phenomenon, and its effects?

Affluents.-The affluents of a river must be mentioned in their proper order, whether proceeding from the mouth upward or from the head or source of the river downward, stating which, and whether the affluents are on the right or left hand. As for the effects produced by them on the river under consideration, all that is necessary to observe on this

These terms Deltic and Ana-deltic, have been approved by a Committee of the Royal Geographical Society, appointed for the purpose of endeavouring to form a precise geographical terminology.