Zoœcia strongly pyriporiform, very small, length about ·4 mm.; areas broadly speaking elliptical but with a strong tendency to have the upper end flattened rather askew to the central line, average length ·18 mm., breadth ·11 mm.; the side walls of the area bear about a dozen tubercles so small that their existence is only just recognizable under a 3 in. objective; a 1 in. objective shows them to be perforated; below the area there is typically (after the early stages) a small perforated boss placed centrally on the front wall, but when the front wall has to accommodate an oœcium the boss splits into two, often very massive, one on either side of the oœcium.

As is well known, the skeleton or oldermass of New Zealand is largely composed of a mass of deformed sedimentary rocks, the precise ages of the members of which are in doubt but do not affect the problem under consideration. The most profound deformation of this vast sedimentary group took place in late Jurassic or early Cretaceous times during what may be termed the “Mesozoic orogenic period”, when probably a great mountain range came into existence.

In this group, shown in the sketch-plan Fig. 4, may be included the interesting pietre verdi areas (1) of the Rocciavré ridge on the right, (2) of Monte Rocciamelone on the left side of the Dora Riparia Valley, and (3) of the Rocciacorba ridge and the Avigliana belt of spurs where the Dora and the Sangone Rivers emerge from the Alps and enter the Po Valley about 20 kilometres west of Turin.

Topaz is commonly supposed to have been formed by the action of fluorine-bearing vapours on felspar, but evidence has recently been advanced with the object of showing that some important veins intrusive in the porphyritic granite of Gunong Bakau, a mountain 4,426 feet high, situated in the centre of the Main Granite Range of the Malay Peninsula, were formed of a rock in which “the topaz and cassiterite are not alteration products of previously formed minerals”. The author of this theory gives the rock the descriptive name of ‘quartz-topaz’, and adds as his reasons for not calling it ‘greisen’ the fact that in places it contains very little mica and that, unlike the majority of greisens, it is not an alteration product.

The British Museum has recently received (in the James W. Butler collection, presented by his daughter, Miss Daisy Butler) a particularly fine mandible of a gigantic fossil Cephalopod. Unfortunately the locality of the fossil is not recorded, but as the collection contained quite a number of specimens from Bradford Abbas (Dorset) and the immediate neighbourhood, and the matrix of this specimen agrees very closely with that of those examples, there can be little doubt that the locality of the fossil is almost certainly Bradford Abbas, or the immediate neighbourhood, and that the specimen is of Bajocian age.

The distribution of land and sea implies that the earth's outer shell is in a condition of approximate hydrostatic equilibrium. Otherwise the equatorial regions should be girdled by a continental protrusion, or else each of the polar regions should be occupied by a continental bulge. The observed fact that the inequalities of the earth's surface exhibit neither of these conditions proves that the general ellipticity of the lithosphere does not differ greatly from that which would be assumed by a liquid spheroid having a similar distribution of density in depth. The incapacity—thus demonstrated—of the lithosphere to endure permanent stresses leads naturally to an inquiry into the conditions that maintain continents and mountain ranges above sea-level. Investigations based on the deviations of the plumb-line from the vertical and on the varying intensity of gravity indicate beyond doubt that the elevated tracts of the globe owe their support to a deficiency of density in their deep-seated foundations, while the great sunken areas owe their depression to a corresponding excess of density in the underlying rocks. Thus has arisen the conception of isostasy, a word which was coined by Dutton in 1889 to express the state of hydrostatic balance that maintains in position elevated and depressed columns of the lithosphere.