This species of knot occurs for all numbers of intersections greater than 2.

9.

2

5

This is the 7 knot which Listing does not sketch. Ante, p. 311. 10.

This is the simple twist, which occurs for every odd number of intersections.

As 2 and 4, 3 and 5, 6 and 7 are capable of being deformed into one another, three of them are not independent forms, and thus the number of distinct forms of seven-fold knots is only eight.

Drawings of various forms of each of these knots were given, as well as indications of the modes in which they can be formed from knottinesses of lower orders.

Monday, 2d April 1877.

SIR WILLIAM THOMSON, President, in the Chair. The following Communications were read :

1. Professor GEIKIE exhibited a large Map showing the progress of the Geological Survey of Scotland.

2. Notice of a Saline Water from the Volcanic Rocks of Linlithgow. By Professor Geikie, F.R.S.

From a boring which has recently been made about a mile west from the town of Linlithgow, water has been obtained differing so much in character from that of the usual wells and springs of the district that some notice of it deserves to be placed on record. When the fact was communicated to me I was asked to explain by what means sea-water could obtain access to underground rocks in an inland district. On visiting the ground I found the site of the bore to be among some hollows of the gravel and sand which cover the country between Falkirk and Linlithgow, its height being about 165 feet above the sea, from which it was distant about three miles. The ordinary wells of the district are situated in the superficial deposits, and supply good potable water, though the supply is necessarily limited. A more copious flow being desired the bore was sunk through the sands, gravels, and clays (here rather more than 100 feet thick), and then entered upon a succession of green, brown, blue, and red "whinstone." After a depth of 317 feet had been passed through, consisting entirely of these alternations of "whinstone," a sample of the tolerably copious supply of water which had now appeared was drawn up and sent for analysis to Dr Stevenson Macadam, whose results were as follow :

This large admixture of saline ingredients rendered the boring unavailable for the increase of the water-supply; but the boringrods were driven 30 feet further in the hope that possibly this mineral water might find some other subterranean means of escape. The hope was of course disappointed, and the operation terminated at a depth of 451 feet from the surface, the lower 348 feet of the boring having been found to pass wholly through "whinstone" in numerous bands of varying hardness and colour. Two samples of the water, taken when the ultimate depth had been reached, were submitted for analysis to different chemists, and gave nearly similar results. The proportions of salts obtained by Mr Robert M'Alley, Falkirk, were the following:

One character of the water not noticed in the analyses, but distinctly perceptible to me in a freshly drawn sample, was the odour of sulphuretted hydrogen. I may add that the bore was begun from the bottom of a previously made well 18 feet from the surface, and that I found the water flowing out abundantly from the top of the bore-tube into the well from which it was temporarily pumped away.

It was evident that the idea of any subterranean communication

with the sea was quite inadmissible. In the first place, the locality is three miles from the nearest part of the sea-coast, with a ridge of high ground intervening. In the second place, between it and the sea-margin lie the numerous deep pits of the Borrowstounness and Kinneil coal-fields, which, it may be supposed, must prevent at least any superficial water-communication. And in the third place, the proportions of the various salts contained in the water are quite different from those which would have resulted from the mere access of ordinary sea-water. The salts can only have been derived from the subterranean rocks traversed by the water.

An acquaintance with the geology of the district enables me to recognise the various kinds of " whinstone found in the bore. They are successive beds of the dull green and brown, usually more or less decomposed, dolerites (diabases) forming the long volcanic range between Bathgate and the sea, and which were poured out partly as submarine and partly as subaërial lavas during the deposition of the Carboniferous Limestone, or Lower Coal series of Linlithgowshire. Occasional bands of green and red tuff mark intervals between the lava-flows. Since the water from the superficial gravels was of the usual potable quality there can be no doubt that the saline impregnation comes from the underlying rocks.

So far as I am aware, the first detection of soda as a chemical constituent of rocks was made by Dr Robert Kennedy, and announced to this Society as far back as December 1798. He analysed the specimens of whinstone employed by Sir James Hall in his classical experiments upon the fusibility of whinstone and lava, and found the constant presence of soda to the extent of four or five per cent., with one per cent. of muriatic acid. He further examined pieces of sandstone from the neighbourhood of Edinburgh and elsewhere, with the invariable result of detecting an appreciable quantity of common salt in them. Since the early date of his researches chloride of sodium has been found very widely diffused among the minerals and rocks of the earth's crust.

There seems to be three chief sources from which rocks derive their chloride of sodium:-1. Rain; 2. The evaporated water of old salt lakes and inland seas; 3. Volcanic sublimations.

1. Rain. The researches of Dr Angus Smith* into the compo

See his Air and Rain.

sition of rain in different parts of the country have shown the very general prevalence of chlorides, and particularly of chloride of sodium, in the air. As might be expected, the proportion of chlorides is greatest nearest to the sea, though abnormally large quantities are found in the air of manufacturing towns as the result of the combustion of coal, &c. On the west side of Britain the proportion of hydrochloric acid in rain was found sometimes to amount to nearly four grains per gallon, or 56 parts in a million. On the east side of Scotland the proportion sinks to 9 grain per gallon, or 12 parts in the million. There can be little doubt that most of this is chloride of sodium. Dr Smith has pointed out the curious fact that this salt cannot be conveyed into the atmosphere merely in spray driven from the surface of the sea by high winds, for if that were the case the composition of the rain should be approximately like that of sea-water. But the saline ingredients do not occur at all in similar proportions. It seems reasonable to suppose that the superficial parts of rocks liable to be saturated with rain-water must thereby receive an appreciable amount of chloride of sodium. In this case it is evident that much care should be exercised in procuring for analysis portions of rock which lie beyond the reach of this surface saturation. Possibly in some of the instances cited by Kennedy, in the paper already referred to, the common salt may have been introduced by the action of rain.

2. The Deposit of Salts on the Floor of Old Lakes and Inland Seas. -This mode of origin is doubtless by much the most important source of the chloride of sodium in rocks. When we consider the large proportion of marine strata in the stratified part of the earth's crust it is surprising, as De la Beche remarked long ago,* that saline waters are not more abundant than they really are. Dr Sterry Hunt has pointed to the mineral waters of Canada and the North-Eastern States as probably deriving their salts from the original sea-water of palæozoic times still imprisoned within the pores of the rocks.† I need not refer to the abundant deposits of rock-salt and gypsum, as well as of saliferous and gypsiferous clays, which occur in so many districts of the world.

2. Volcanic Sublimations.-The occurrence of incrustations and * Researches in Theoretical Geology. "Essays in Chemical Geology, 1875."