6. Recent silt containing Scrobicularia piperata in Post-Glacial 7. Sand containing Tellina, Turritella, &c., forming shore of the River Mersey. Nos. 3 and 4 were divided from each other in places by a bed of peaty matter a few inches in thickness, which I consider of no geological importance. It is quite evident that the gulley, as shown in these sections, could not have been excavated by the stream under present conditions of level of land and water. The inference from this and numerous other examples which it is not necessary to detail here, is that when the gulley was excavated in the Boulder-clay the land stood higher than at present. At Dove Point, Cheshire, was to be seen, and probably still is, a land surface corresponding to this period (see section M to N, Detail sheet of Sections in PostGlacial Geology of Lancashire and Cheshire), with the Scrobicularia clays (Formby and Leasowe Marine Beds) lying upon it, and above that another land surface representing the Main beds of peat with stools of trees in situ. If we follow out the chain of events of which these remains are the consequences we shall find that the gullies in the Boulder-clay and rock and the Lower or Inferior peat represent a period of elevation of the land (of undetermined extent), the Marine silts a period of depression, and the Main or Superior peat bed another period of comparative elevation, as proved by the Submarine forests on the coasts of Lancashire and Cheshire, and the recent silts a subsequent and final depression. All these former land movements I consider are clearly established by the evidences of various sections I have had the opportunity from time to time of personally inspecting. Of the limits of their horizontal extension it is impossible to speak with so much certainty, but, from the numerous examples of peat beds and stools of trees found at almost every estuary in Great Britain, from the Land's End to the Orkney Islands, and from similar examples to be found in Ireland and on the coast of France, two of the movements must have been very widespread. The problem I would wish to place before Irish Geologists is this -Are there evidences of land movements, similar to those I have described on the West Coast of England, to be found in Ireland? and if so, to what extent? No very detailed account of the Post-Glacial deposits of the estuaries of Ireland has come under my notice; but I trust that when attention has been called to this subject it may be worked in a more systematic manner; as it is probable much light would thereby be thrown on the period of time subsequent to the Glacial era. Mr. Kinahan, in his Manual of the Geology of Ireland, in a chapter on "Submerged land and forests," mentions various examples of peat with tree-stools in situ occurring below high-water mark, and states that on the East Coast different beaches of this age (the 12ft. beach) lie on the submerged peat, proving that the twelve-feet beach was formed more recently than the submergence." As Professor Hull and Mr. Kinahan adopt a different classification of the raised beaches, it is not always easy to identify them, but I presume the "twelve-feet beach" of Kinahan is "the continuation of the twenty-five-feet beach of Scotland" of Hull.* Mr. Kinahan also refers to a submerged bog, "discovered by Dr. C. Farran at Clonca, near Dungarvan, after one of the highest tides known in the country." "Here are the remains of an ancient pine forest, miles in length, now usually covered with many fathoms of water." I think it extremely probable that these submerged forests of Ireland are synchronous with the Main or Superior peat-andforest-bed of Lancashire and Cheshire. This often has, as in Wallasey Pool, the site of the present Birkenhead Docks, a considerable depth of recent marine silt lying upon it, in which we find horns of the red deer, bones of cetaceans, and other mammalian remains. The surface of this silt is so little raised above ordinary high-water level that it must have been laid down approximately at the present levels of land and water. As we go Physical Geology and Geography of Ireland. further north there does, however, appear to be evidences of the land having been lower than at present. There is the raised beach, or rather shell-bank, on the shores of Morecambe Bay, a few feet above high water; and at St. Bees, further north, I found in 1872 what I consider Post-Glacial deposits, corresponding to the Formby and Leasowe Marine Beds, at an elevation of from eight to nine feet above high water. All these facts point to a gradual elevation northwards; and in the estuary of the Tay and other Scotch rivers the "links" consist of sand and silts overlying peat, containing remains of trees. It is, therefore, not improbable that this may be the result of one earth movement. If my supposition be correct the raised estuarine deposits of Scotland are subsequent to the Superior peat-and-forest-bed of the North-West of England, and synchronous with the last of the raised beaches (containing worked flints) of the east coast of Ireland; and the more recent of the marine silts, such as those of Wallasey Pool, overlying the Superior peat-and-forest-bed, are of the same age. Should these suppositions prove correct it now remains to discover if there exist in Ireland the equivalents of the Formby and Leasowe Marine Beds, which underlie the Superior peat, and also the remains of the land surface upon which I have shown they rest. If these few observations should induce any of the Irish geologists to turn their attention to the subject, I shall be very glad, and I am quite sure it is well worth investigating. The Last Geological Changes in Scotland (Jameson), Quarterly Journal of Geo. Soc. for August, 1865, pp. 188-190. XXXIX.-NOTES ON THE ANNUAL WATER-DISCHARGE OF LARGE RIVERS; WITH INDICATIONS OF SOME NEW HAUGHTON, M.D., D.C.L., F.R.S. [Read May 19th, and June 16th, 1879.] NOTE I. On the Annual Water-discharge of the Ganges, Brahmapûtra, and Irawady. The Rev. Mr. Everest, in 1831-32, instituted a series of observations and experiments on the Ganges, at Ghazipûr, a little below Benares, and 500 miles from the mouth of the river, at the Hoogly. From these experiments, the following facts were obtained :— The arithmetical mean of these figures for the whole year is, obviously, 203,485 cubic feet per second; which gives us an annual water-discharge of 43 625 cubic miles. Now, the total length of the Himalayan ridge drained by the Ganges is 670 miles, and the rainfall increases from west to east: but the Ganges, at Ghazipûr, has received the drainage of only 150 miles of the western end of the ridge. Sir Charles Lyell, following Colonel Strachey, proposed to estimate the discharge of the Ganges into the sea by increasing the Ghazipûr discharge, in the proportion of 670 to 150, or to nearly 4 times the Ghazipûr discharge.* As this appears to me a very rude method of calculation, I have recomputed the areas of the rain-basins of the Ganges, above and below Ghazipûr; and of the Brahmapûtra, using for the purpose Mr. Stanford's newest Orographical Map of Asia. I traced carefully, for this purpose, the three areas mentioned, * Principles of Geology (Lyell), vol. i., p. 480: London (1875). SCIEN. PROC., R.D.S. VOL. II., PT. IV. T and also the area on the map lying between 20° and 30° latitude, and within 10° longitude. The tracings were then carefully cut out and weighed, with the following results: (1.) Rain-basin of Ganges above Ghazipûr = 0.5150 (3.) Rain-basin of Brahmaputra (weight of tracing) (4.) Standard area (weight of tracing) I calculated the standard area at 325,660 sq. geo. From the above we readily find. miles.* Total Rain-basin, Brahmaputra. 292,140 geo. miles. This result gives a total discharge for the Ganges somewhat more than double the Ghazipûr discharge (instead of four or five times), or, exactly— Annual Discharge 97-170 cubic miles (statute). = The dry season discharge of the Brahmapûtra, at Gwalpara, near the head of its delta, is given by Major Wilcox,† as 150,000 cubic feet of water per second; and I have calculated (by reducing Everest's discharge of 36,330 cubic feet per second, of the Ganges, at Ghazipûr) the Gangetic dry-season discharge at a point corresponding with Gwalpara, on the Brahmapûtra, to amount to 76,000 cubic feet per second. If we adopt this ratio, we find, for the probable * By integrating the expression r2 sin 0 de dp between the limits named, where r-radius of earth in geogr. miles=3958 x 60 69-1' 0 north polar distance † Asiatic Researches, vol. vii., p. 466. |