levelling operations of the Revenue Survey with those already completed, or about to be prosecuted, by the Irrigation Branch of the Public Works Department.

The field mapping is all executed on a scale of 4 inches to the mile.

In addition to the regular professional revenue survey of villages, there has always been a minute measurement of fields for assessment purposes, conducted by native agency, entirely under the collector or settlement officers. These are crude operations after native fashion.

In the presidencies of Madras and Bombay, minute cadastral measurements of fields are in progress under European officers; these surveys are essentially for settlement and revenue purposes, and have no connection with the Indian Survey Department, nor are they under the direction of the Surveyor-General of India.

Topographical Survey.-The Topographical Branch of the Indian Survey Department is under the immediate superintendence of the Surveyor-General of India, and had its origin in the Revenue Survey. Its operations are confined chiefly to hilly and junglecovered ground, yielding but little revenue, in parts of the country not actually under British management, and in friendly native states along the British frontier; and its object is to obtain a cheap, rapid, and reliable first survey for geographical and administrative purposes. The groundwork or basis of its operations is secondary and minor triangulation dependent on the Great Trigonometrical Survey operations, from which all the initial elements of latitude, longitude, elevation, distance, and azimuth are derived. The triangulation is carried on in a network covering the ground with points or stations at about 3 to 4 miles apart. The instruments employed for the secondary triangulation are vernier theodolites with 12 and 14 inch azimuthal circles; the horizontal observations are taken on four zeros repeated and the vertical angles on two zeros. For the subsidiary or minor network of triangles, theodolites with 7 and 8 inch azimuth circles are used, and the angular measurements are made with two zeros repeated.

The detail work, or delineation of the configuration of the ground, is executed usually on the scale of 1 inch to the mile by means of the plane-table. Some topographical surveys in cultivated or valuable tracts are on a scale of 2 inches to the mile; and a few others, in very broken and wild ground, on a scale of 2 miles to the inch. In addition to the 1-inch survey, the Topographical Branch undertakes the plans of all the important cities, forts, and strongholds in native states; these are mapped on scales varying from 6 to 16 inches to the mile.

Asiatic Researches.

REFERENCES.

Vol. VII.

1803.

Edinburgh Review. Vol. XXI. 1813.

Calcutta Review. Vol. IV. 1845.

Everest's Measurement of the Meridional Arc of India. 1847. Calcutta Review. Vol. XVI. 1851.

Trigonometrical Survey (India). Printed Parliamentary Paper. No. 219 of 1851.

Report on the Survey of India for the three years ending 1858–59. By Lieut.-Col. Sir A. S. Waugh. 1861.

General Reports on the Operations of the Great Trigonometrical Survey of India. 1862-63 to 1868-69.

Professional Papers on Indian Engineering.

and IV. Published at Roorkee.

Vols. II., III.,

Report on the Cartographic Applications of Photography, and Notes on the European and Indian Surveys. By Lieut. J. Waterhouse, R.A. Calcutta, 1870.

III. THE GEOLOGICAL SURVEY OF INDIA.
(With a Sketch-map.)

By H. WOODWARD, F.G.S.

SIXTEEN years have now elapsed since the Geological Survey of India commenced its systematic labours, and it may now be interesting to give some account of the progress that has been made, and to note a few of the results to which the Government officers have been led.

Some time beforehand, in 1851, Mr. (now Dr.) T. Oldham, the Superintendent of the Survey, arrived in Calcutta.

The work which he was then required to do was to go from place to place, and, without loss of time, to search for coal and other minerals of economic value; to furnish reports, and thus to indicate by observations in a few places the important results that might be obtained from a detailed survey of the whole of the country. Great were the difficulties with which he had to contend at the outset, and for a long time afterwards; so that not until 1856 was he able to establish that regular system of operations carried on by a staff of officers, small at first, and even in 1863 numbering but fifteen geologists.

No one was better fitted for the task in hand than Dr. Oldham; he had been Local Director of the Geological Survey of Ireland, and was previously Professor of Geology in Trinity College, Dublin.

With his small band of Geologists, the Survey was carried on with vigour, and periodical reports were published, accompanied by maps, geologically coloured, and sections of the country described.

The value of the establishment was soon appreciated by the public, and numerous applications for reports on geological matters were made, as well as for aid in analyses of coal, minerals and ores, of soils, water, and in assays. Such information and assistance was given to many private individuals, as well as to Government departments and to companies.

The earlier observations were, as might be expected, fraught with much difficulty. But few and isolated notices, compared with the size of the country, had been written upon it. The labours of Dr. Carter, of Bombay, of the Revs. Hislop and Hunter, Presbyterian missionaries in Tinnevelly, and some others, had certainly done a little towards paving the way for a classification of the rocks; and Mr. Greenough had, in 1854, after many years' labour in compilation, prepared a map of India, upon which he had depicted all that was then known concerning the geology of the country.

*

Dr. Oldham, however, found it necessary to establish several new groups to receive (provisionally) the various rocks that were met with, inasmuch as for many-and these some of the most widely-extended and important groups of rocks-there was no definite horizon from which to work either up or down. Over thousands and tens of thousands of square miles not a fossil was found, save some vegetable remains, affording, at the best, but very imperfect evidence. The richly fossiliferous rocks of the Himalaya and Sub-Himalaya being widely separated from all the rocks of the Peninsula by the broad expanse of the Alluvium which unites the valleys of the Ganges and Indus, it was impossible to trace out, by their aid, any superposition.

To endeavour to remedy this, it was found advisable to examine many distinct tracts, and to make more or less rapid observations on distant parts, which, although interfering with the continuous progress of the Survey, were generally of essential service in leading to definite results on important geological points, which, in the ordinary progress of the work, could not have been arrived at for many years to come.

The climate of India necessarily restricts the work to certain portions of the year. The working season lasts about seven months, and differs very materially in the southern part of the Peninsula from that in Bengal. In the latter district, the close of the Indian financial year (the 31st March) nearly coincides with the close of the field season. In Madras the season is then not half over.

* See Mr. Horner's Anniversary Address to the Geological Society of London. 1861. 2 I

VOL. VII.