period at which the great canal maker of India, the Emperor Feroze, was employed in the construction of the work which still bears his name.

Subsequent years saw a gradual development of the systems of irrigation, both in Lombardy and Piedmont, but they were for a long time administered in a very rude and imperfect way. No surveillance was exercised over the distribution of the waters, and every man supplied his own wants very much according to his own wishes. In the year 1474 the first indications appear of a regulated outlet being applied to the canal of Ivrea, in Piedmont, which, though of a rude plan at first, became modified and improved step by step, until the metrical module of the present day was arrived at.

Soon after the North-western Provinces of India came under the British Government, the propriety of restoring the Mogul canals began to be agitated. Attention, it is said, was first drawn to the subject by the offer of a Mr. Mercer to re-open the Delhi canal at his own expense, on being secured the whole proceeds of it for twenty years. This offer was declined, and about the year 1810 several officers were deputed to survey and report upon the lines both east and west of the Jumna. The subject was, however, soon dropped, but it was resumed with characteristic vigour during the administration of the Marquis of Hastings, who, in 1817, appointed an officer to superintend the restoration of the Delhi canal; and in 1822 another officer was deputed to survey and report upon the Doab canal. Similarly, in Southern India, the works of the natives were followed up and improved upon soon after the acquisition of the country. The hopeless state of confusion into which the Tanjore Government had fallen having led to the cession of the country to the English in 1801, the maintenance of the works of irrigation in that province, of course, devolved upon them from that time forward; and it was not long before certain defects inherent in the system began to exhibit themselves in a very clear and unpleasant manner.

The earlier works of this character, undertaken by the British in India, were, almost without exception, the restoration of ancient native works, and the defects originally existing in their construction were too often followed and imitated. On the Ganges canal, for the first time, was any entirely original work of this class attempted. Ground was broken on the 16th April, 1842, and the canal was opened, by the admission of water, on the 8th April, 1854.

It would carry us beyond the limits of a single paper were we to attempt to trace down the continued progress of irrigation works from the period of their revival in the different countries to which reference has been made in the foregoing pages; we shall, therefore,

conclude this brief historic account of artificial irrigation by a short description of some of the methods adopted in their construction.

All canals taken off from rivers require a dam to be constructed across the stream, just below the point of their debouchure, and there are two distinct systems of this canal irrigation in ordinary practice, according to the nature of the country to be irrigated, and its physical peculiarities. The high table-land lying at the foot of mountain ranges, as in Northern Italy and North-western India, requires the adoption of a system very different from that pursued in the delta lands of the coast, as in Eastern Spain and Madras. The latter system consists in throwing a dam across the bed of the river, to raise the surface level of the water, which is then conducted along canals, whose mouths are above the dams, to the lands requiring it. This system is necessarily confined to alluvial tracts, which have been formed by deposits from rivers in a state of flood. In the former case, it is necessary to go back to some point high up in the river's course, whence the water can be brought on to the high land by excavation of a moderate depth, and by which sufficient command of level may be obtained to overflow the surface.

The simplest kinds of canals are those which are generally known as Inundation Canals, many of which exist in the Punjab and in Sindh, and by which the low-lands adjoining the rivers in those provinces are irrigated. Cuts are made from the river inland, for a certain distance, and are then carried in a direction generally parallel to the fall of the country, or the course of the river. By these, when the latter is in flood, the autumn crop is watered, but in the cold season, when the river is low, the canals run dry, and the spring crop thus derives no benefit from them. There are no works at the head of such canals to control the supply of water, for the course of the river Indus is so uncertain that it may completely desert the head, and the water may have to be brought in by a new mouth excavated for one season, which again may be useless in the next.

The Lake system of Irrigation is common to the plains of Lombardy as well as to the Madras Presidency. Where its introduction is practicable, this is, no doubt, a far more economical method of applying artificial irrigation, than the construction of large canal works; the former requiring generally but small expenditure, whilst the cost of the latter is run up by the numerous subsidiary works required for their completion. It does not appear necessary to say more with reference to these works; we shall therefore conclude the present article with a further notice of those subterranean channels to which we have already referred. Wellsted, in his Travels in Arabia,' describes this method of irrigation, as it is practised in the Bediah and other oases of Omán. He says:"The oases of Bediah, and nearly all those of the interior of Omán,

owe their fertilty to the happy manner in which the inhabitants have availed themselves of a mode of conducting water to them, a mode, as far as I know, peculiar to this country. The greater part of the face of the country being destitute of running streams on the surface, the Arabs have sought in elevated places for springs or fountains beneath it. By what mode they discover these I know not, but it seems confined to a peculiar class of men who go about the country for the purpose; but I saw several which had been sunk to a depth of 40 feet. A channel from this fountain head is then, with a slight descent, bored in the direction in which it is to be conveyed, leaving apertures at regular distances, to afford light and air to those who are occasionally sent to keep it clean. In this manner water is frequently conducted from a distance of 6 to 8 miles, and an unlimited supply is thus obtained. These channels are usually about 4 feet broad and 2 deep, and contain a clear rapid stream. Few of the large towns or oases but had four or five of these rivulets, or feleji, running into them, The isolated spots to which water is thus conveyed possess a soil so fertile, that nearly every grain, fruit, or vegetable common to India, Arabia, or Persia, is produced almost spontaneously." In the 'Journal of the Asiatic Society of Bengal,' the same subterranean irrigating channels are referred to as being used in Affghanistan, where they are called Kahrezas. Cieza de Leon, writing between 1532 and 1550 A.D., says, "The Indians of Peru had, and still have, great works for drawing off the water, and making it flow through certain channels. Sometimes it has chanced that I have stopped near one of these channels, and before we had finished pitching the tent, the channel was dry, the water having been drawn off in another direction, for it is in the power of the Indians to do this at their pleasure." Markham, referring to these works of the Yncas of Peru, states, "Trenches are cut along the whole length of the valley, becoming tunnels at the upper end, and penetrating into the rocks until they come in contact with underground springs. They are some 4 feet in height, with the floor, sides, and roof lined with stones, and are called huirca. At intervals of 200 yards there are man-holes in the main tunnels."

Somewhat similar works are also referred to in Baird Smith's Italian Irrigation, under the designation of Fontanili, as existing throughout the irrigating districts of Piedmont.

REVIEWS OF SCIENTIFIC WORKS RECENTLY PUBLISHED.

A Journey in Brazil (Agassiz). Rambles of a Naturalist on the Shores and Waters of the China Sea (Collingwood). Acadian Geology (Dawson). Coast Defence (Von Scheliha). Minor Works and New Éditions.

A JOURNEY IN BRAZIL.*

IN the winter of 1865 Professor Agassiz found it necessary to seek a change of scene and climate, and rest from work. From early life he had possessed a desire to study the fauna of Brazil, and especially the fishes, in their own home. Single-handed he would have been able to make but slight use of the opportunities presented to him during a visit to that country, although he was certain that the Emperor and the head of his government would give him every facility for his investigations.

While brooding over his difficulty, Mr. Nathaniel Thayer expressed to the Professor an interest in his proposed journey, and said, "Take six assistants with you, and I will be responsible for all their expenses, personal and scientific." This princely generosity was carried out in its largest and most liberal sense; and thus we have the origin of Professor Agassiz's Scientific Expedition to Brazil.

The volume before us contains a sketch of the Journey in the form of a diary, with here and there statements of the results of the investigations of the party: it is well calculated to interest general readers who are curious in such matters as the manners and customs of a wandering naturalist.

The voyage out was occupied most instructively: the Professor gave lectures to his assistants on various Natural History subjects, including the Gulf Stream and its Inhabitants, the Physical features of South America, Embryology, the Glacial Period, the Art of Observation, and many other subjects bearing upon the work before them, concluding with a warning against Darwinian tendencies; brief reports of the lectures being here given by Mrs. Agassiz.

Landing at Rio de Janeiro, the route of the expedition was up the coast to Pará; up the Amazon to Manaos, and on to Tabatinga, the frontier-town between Brazil and Peru: having left one of their party at that place to make collections, and two at San Paolo, the

* A Journey in Brazil.' By Professor and Mrs. Louis Agassiz. 8vo, pp. 540. Boston: Ticknor and Fields; London: Trübner and Co., 60, Paternoster Row. 1868.

remainder returned down the river as far as Teffé, where they remained nearly a month, journeying back then to Manaos, which they made their head-quarters and general rendezvous. After the reassembling of the party, and after making some excursions on the river Ramos and the Rio Negro, their steps were retraced to Pará, and thence to Rio. Remaining in the capital, and exploring its neighbourhood, for about three months, the expedition returned to New York after a sojourn of fifteen months in Brazil.

The known results of this expedition are too numerous to mention even in a review, and many facts and conclusions of the highest importance still remain to be worked out and verified before any cautious naturalist would venture to publish them. The chief object of the expedition was to ascertain how the fresh-water fishes are distributed through the great river-systems of Brazil; and all the excursions and independent journeys were planned in reference to this idea. Professor Agassiz estimates the number of species of fresh-water fish collected by the members of the expedition at between 1800 and 2000, or nearly twice as many species as exist in the Mediterranean. The number, however, is not so astonishing as the distribution. From Tabatinga to Pará the river differs neither in the temperature of its waters, in the vegetation of its banks, nor in the nature of its bed; yet under these circumstances completely distinct assemblages of fish are met with from distance to distance. When we consider that all the rivers of Europe united have not yielded more than 150 species of fresh-water fish, and that Professor Agassiz found in one small pond, covering about 400 or 500 square yards, no less than 200 species, mostly peculiar to that spot, we are inclined to indulge in a little scepticism. We want to know how many genera and families are represented by these 200 species, and what degree of affinity there is between the species themselves. Remembering Professor Agassiz's extreme opinions in favour of the theory of special and direct creation of species, we cannot help regarding it as possible that his "species" are not all entitled to that dignity. If they are, and are closely related, the explanation may be that the process of variation is stimulated in a vast degree by the tropical climate and physical features of the region. If both these suppositions are erroneous, we have here a Natural History marvel entirely without precedent; for we presume that the majority of Mr. Lea's species of Unionidæ, the only comparable example we know of, would be regarded as varieties by most European conchologists.

Another "sensation" discovery is that of the evidences of the Glacial Period in tropical America. Every geologist knows that the crystalline rocks of South America are extensively decomposed at the surface; but Professor Agassiz states that although the received explanation is true to a great extent, yet that a consider