has become more rare, and now breeds only in some favoured localities, where it is pretty safe from molestation.

In Ireland it is also far from common, but is known to breed on some of the lakes there.

In Scotland it is met with frequently in the winter, principally on the east coast. Mr. Gray, in his "Birds of the West of Scotland," says that the Crested Grebe has come less frequently under his notice than any of the other Grebes. On the Tay, Colonel Drummond Hay considered it as only a winter visitor, although he mentions a pair that were supposed to have been shot on Loch Ordie in full breeding plumage.

Records as to the Crested Grebe having bred in Scotland are extremely meagre, and in the Society's Library I have come across only one really authentic record of the nest and eggs having been found. The record I refer to is from the Lake of Menteith in Stirlingshire, in the year 1896, and from the rarity of its occurrence, and the graphic account given by Mr. Lee of the nesting habits of the bird, I am tempted to borrow the following:

"In the spring of 1895 I observed a pair of Crested Grebes on the Lake of Menteith, but failed to locate their nest. On the 28th April, 1896, however, I arrived at the lake, determined to find the nest if it was there, and was rewarded by seeing a fine male in full breeding plumage diving about near a large bed of reeds. He was very tame, and allowed me to row within thirty yards of him without paying the least attention to me, so that I had ample leisure to admire him through my glasses. I failed, however, to find the nest that day, so on the morning of the 29th I started early, as I was quite sure that the female was sitting on eggs not far off. I commenced operations by beating up the reeds, and as I came close to a swan's nest, I saw a tell-tale ripple and line of bubbles running out from a point among the reeds, just like some big pike making off to deep water, and to my delight the female Crested Grebe appeared about seventy yards off. In less than three minutes I had found the nest. It was rather an insignificant pile of dead reed stems, decayed weeds, and freshly plucked water-lily leaves, floating in about two feet of water among the tall reeds, and anchored to them. It contained two eggs, which were carefully covered up and felt quite warm.

"After disposing of my boat at some distance I waded in among the reeds and hid myself behind a thick clump about fifteen yards from the nest. I could see the two Grebes out in the open water, abouty eighty yards off. They sat low in the water, and the male would now and then swim round about his mate, ducking and bobbing his head, and striking the water with a stroke of his wing. The female, however, paid little attention to his blandishments, as her eye

was fixed on the vicinity of the nest. They swam about in the same spot for about half-an-hour, and, just as my patience was becoming exhausted, the female swam closer inshore, and after looking cautiously about, she dived.

"I kept my eyes glued on the nest, and suddenly she appeared about three feet from it, but must have seen me, as she dived almost immediately, and reappeared about forty yards off. I changed my position, getting further behind the reeds, and in about fifteen minutes she suddenly appeared again beside the nest, and after a hurried look round, got on to it, and carefully uncovered the eggs, arranging all the weeds on the nest before she finally turned the eggs with her bill and settled herself on them. The male appeared immediately after, about six feet from the nest, with a young water-lily leaf in his bill. This he deposited on the side of the nest, the female giving it two or three playful dabs with her bill.

"After he dived away the female composed herself to rest, and buried her head among her feathers. By this time I was getting very cold and stiff, as I had been standing in the water for about two hours without waders. Keeping my eye on the sitting bird I made a slight movement, She jumped up and hurriedly covered up the eggs, remaining bolt upright, with head erect, and listening intently as if she had not spotted me. On my next movement she dived noiselessly into the water, and appeared about sixty yards off in the open water. I was so cold and stiff that I could hardly wade ashore, but I was amply rewarded by my glimpse at the habits of these beautiful birds at their nest."

The bird here exhibited was shot by Mr. Cox on the loch where we got the two nests, and is a young male not yet in full plumage. But this other bird is an adult male, and exhibits the Crested Grebe in full feather. I am sure many of the ladies present will recognise in the beautiful satiny breast of the Grebe the material from which the muffs and collarettes were formed some years ago, but, happily for the Grebe, they are at present out of fashion, and may they continue to be so; and I am sure, that under proprietors like Mr. Cox, the Crested Grebe may be induced to extend its breeding boundaries in the county, and to become as familiar an object on our Perthshire lochs as it is now rare.

X.-The Agates of the Sidlaws.

By R. Dow, Schoolhouse, Longforgan.

(Read 13th April, 1905).

THE SIDLAWS.

As the student of field geology wanders in search of science and of scenery among the solitudes of the Sidlaws, the contrast between the peacefulness and the beauty of the landscape to-day and the geologic past now long gone by, when volcanic fires were in action, when streams of liquid fire deluged and desolated the landscape, is powerfully impressed on the imagination.

The great volcanic ridge across the midlands of Scotland continues almost unbroken in the Campsie Fells of Stirling and the Ochils of Perthshire. In the vicinity of Perth, this persistent ridge branches into two divergent portions, one of which runs on through the north of Fife until it sinks in the ocean at Tayport, while the other, after sinking beneath the alluvial deposits of the Earn and Tay, mounts once more into the precipitous cliffs of Kinnoull Hill, and thence stretches eastward into Forfarshire as the Sidlaw Hills.

The rocks of the Sidlaws consist of successive sheets of andesite lava, of the familiar types easily recognised in hand specimens, and varying in colour through shades of blue, purple, and red, and in texture from a dull, compact, almost felsitic, or micro-granular character, to more coarsely crystalline varieties. The sheets are often amygdaloidal, especially in the upper and lower portions of the individual flows. These lava flows are not infrequently separated from each other by courses of conglomerate, sandstone, and grit. Of these, four are of sufficient thickness and persistence to be mapped, and are shown on the Geological Survey Sheet No. 48. The pebbles of these intervening conglomerates range up to blocks 2 ft. in diameter, and consist chiefly of andesites, but include many pink felsites and pebbles of greenish sandstone. These alternating sheets of sandstone and lava clearly demonstrate that the volcanic fires, which gave rise to the Sidlaws, ranged over immense periods of time, probably throughout the entire Old Red Sandstone Age.

Another interesting proof of the volcanic origin of the Sidlaws is the neck of one of the volcanoes to be found at Over Durdie. It is 500 yds. in mean diameter, and is plugged with pinkish granular tuff full of andesite blocks. It remains still one of the unsolved local geological problems, why these volcanic necks are so sparse in the

Ochils and Sidlaws, and yet so numerous in the old volcanoes of the carboniferous system of Fifeshire.

But this volcanic neck, and a similar, though much smaller, one some distance to the south-west, remain as unimpeachable witnesses that the volcanic fires, now quenched, once were in fierce action, though now quiescent for geological æons. The lava streams that once descended from these cones have been cut into ravines, and isolated into separate hilly masses, by the streams that have deeply trenched them.

AGATES.

Ruskin, in the preface to "The Stones of Venice," makes this observation, "It is not easy to be accurate in an account of anything, however simple; zoologists disagree in the description of the curve of a shell, or the plumage of a bird, though they may lay their specimens on the table and examine them at their leisure." And I venture to think that this may be said with equal truth regarding Scotch agates. In shape, in colour, in markings, their forms are quite bewildering.

"With figured veins its various surface strewed,

Painted by Nature in a sportive mood;

Strange to relate, 'twas to no artist due,

Nature herself the wondrous picture drew."

Beautiful and precious stones have always had a strong fascination. In the dawn of history they were regarded as magical charms, protecting the wearer against all kinds of mundane evils; by a slight transition, denoting, however, considerable progress, they were regarded as possessing medicinal powers; and finally, by a further transition, leading up to our own times, they have, with the everwidening sweep of true scientific inquiry, been the objects of much investigation.

The highly cultured Greek had full faith in their occult power, and they are frequently referred to by classical writers. Orpheus, in his ode on gems, refers to them as the highest gift of Jove to mortals, bestowed as a sure remedy against all earthly woes, and hidden by the gods underground in mystic caves, and those who find them will be rewarded by endless blessings, and to them care and sorrow will be unknown. In specifying the virtues of each individual gem, Orpheus thus writes-"If thou wearest the agate stone on thy hand, the immortal gods will be ever pleased with thee; and if the same be tied to the horns of thy oxen, when ploughing, or round the ploughman's sturdy arm, wheat crowned Ceres will descend from heaven with full lap to throw the grain upon the furrow." This belief in stones

as charms, dating back to remote ages, still flickers on in this scientific age.

There is something very attractive about a good polished specimen of an agate, or, to give it its more familiar name, a Scotch pebble, as a glance at the fine collection gathered by the late Professor Heddle, now in the National Scottish Museum, Edinburgh, will show. The great majority of agates show almost endless combinations of cream colour, delicate pearl grey, slate colour and lavender tints, while the infinite variety of pattern in which these are arranged delights the eye of those who regard them simply as objects of beauty. But to the inquiring scientific mind the problem of how these patterns and tints were formed is still more interesting.

It is no simple matter to find out in what way Nature worked in elaborating these beautiful agate patterns. There have been many guesses into the secret, and much scientific thought has been expended in the endeavour to clear up the mystery. Many of the problems remain still unsolved, but by the extensive researches of Prof. Heddle considerable advance has been made. It hardly need be stated that a full account of the principles upon which Nature has fashioned them would involve extensive reference to chemistry and physics. But for the present a general idea of their nature must suffice.

The lava cools, it ceases to boil, and at last we have a solid rock, containing many cavities of various shapes and sizes, which are the casts of the steam bubbles, arrested in their ascent and imprisoned by the thickening lava. Hence the shape of an irregular ovoid, originally spherical, but drawn out as they rose in the flow of the viscous fluid. Up to this point geologists agree as to the history of the lava and the cavities in which the agates are formed. In the main, too, they agree that the agate material is deposited from an aqueous solution in layers upon the walls of the cavities by secretion, segregation, or infiltration of such solution. Beyond this point, however, there are two distinct theories. We may call them the hot and the cold water theories. Hot water containing an alkaline solution dissolves silica (the material from which agates are formed) very freely. Cold water containing alkali is a poor solvent of silica. The hot water theorists hold that the formation of agates was therefore contemporaneous with the formation of the lava. The lava contained much highly heated water, which was probably, and almost certainly, saturated with siliceous or agate material. As the lava cooled, the water collected in the vacuous cavities, depositing layer after layer of silica in the form of chalcedony.

The cold water theorists maintain that the lava was cold, and the steam cavities empty to start with. Percolating rain water slowly sank from the surface of the rock, dissolving on the way down a very small