As already stated in the first part of this paper, a regular gradation may be traced from the cassiterite-wolframite lodes to wolframite-quartz veins without cassiterite, a type which appears on the whole to be more common in America than elsewhere. In many cases this difference is clearly due to a more complete differentiation of the magma, but in other instances a purely igneous origin is less conclusively established. In Cornwall and other granitic areas a tin-wolfram lode can sometimes be traced continuously into a wolfram lode, and this again into a pure quartz vein. Here the pegmatitic origin of the lodes is demonstrated, and as a rule the wolfram is accompanied by'fluorite and other recognized pneumatolytic minerals, as well as by sulphides similar to those found in the tin lodes. Thus the genetic connexion with the tin-bearing types is beyond doubt. In a few instances only wolfram is found in association with gold ores; the significance of this will be discussed in a later section.

In the district north of Ashby-de-la-Zoueh dolomitized Carboniferous Limestone crops out where the Leicestershire border adjoins that of South Derbyshire. The dolomites, which attain a thickness of nearly 900 feet in this area, have hitherto received very little attention. I therefore propose to give a short description of them with a view to ascertaining how far their mode of occurrence and structure afford additional examples of, or exceptions to, the usual conclusions adopted concerning the origin of dolomite. With this object in view I propose to give a brief resumé of the evidences generally relied upon to explain the origin of dolomite, before proceeding to describe the Leicestershire rocks.

Shells with the external aspect of Bouchardia have been known for some time from the New Zealand Tertiary (Oamaruian), and were first described by Hutton in 1905 under the names of Bouchardia rhizoida and B. tapirina. The correctness of this generic ascription was doubted by von Ihering, who stated that the shells lacked the characteristic external form of Bouchardia. In this, however, von Ihering was mistaken, probably owing to the unsatisfactory nature of Hutton's figures, for these species agree externally with Bouchardia in the very characters which he supposes they lack, viz., the very sharp beak ridges, the more or less straight sides, and the presence of a longitudinal cord over the suture of the deltidial plates. The most characteristic external feature of the shell of Bouchardia is that the sharp beak ridges unite in an apex dorsally of the foramen, i.e. the foramen is epithyrid. In Hutton's supposed Bouchardiæ the foramen is permesothyrid, but almost epithyrid.

Since Salter, in 1865, published his classification of the species of the genus Homalonotus, no detailed attempt has been made to re-arrange the increased number of species now known into natural groups. Salter was not convinced that his scheme was satisfactory, and appears to have regarded it as largely artificial, though convenient. The divisions instituted or recognized by him bore the names Brongniartia, Salter, 1865 (divided into two sections); Trimerus, Green, 1832; Kænigia, Salter, 1865; Dipleura, Green, 1832; and Burmeisteria, Salter, 1865.

In an article by Dr. H. Jeffreys in the Geological Magazine for April, pp. 215–19, an attempt is made to show that the discovery of radio-active materials in the earth's crust favours the “contraction and puckering” theory of mountain building. With regard to 0. Fisher's view he writes, “It rests entirely on Kelvin's theory of the cooling of the earth, which has had to be completely revised on account of the discovery of the extensive distribution of radio-active matter in the earth's crust. The time available has been found to be about twenty times greater than on Kelvin's theory, and the cooling has therefore had time to extend to a much greater depth and to produce a very much greater compression.” We are also told what the reduction in the earth's diameter has probably been, and the actual depth of Fisher's level of no strain.