The conversion of augite or hornblende into brown mica appears to take place from three causes:—

1. By crushing of pyroxenic minerals and felspar, as has been observed by Professor Bonney in sundry schists of the Alps.

2. By the intrusion of felspathic material into a rock containing augite or hornblende, as in the Harz, where granite invades diabase, converting the augite into biotite. A similar change has been observed in the gabbro of the Barnavave Mountain, in the Carlingford district, the diallage being wholly or in part replaced by biotite owing to the invasion of granophyric magma. In Sark the intrusion of an aplitic magma into almost pure hornblende has resulted in the formation of biotite.

The following particulars of a boring for water made at Puys, near Dieppe, in 1898 have been communicated to me by Messrs. Legrand and Sutcliff, and as they appear to indicate a succession of beds very similar to that occurring beneath Dover, the present seems a fitting occasion for placing on record a brief account of the boring.

The name Nautilus clitellarius was given by J. de C. Sowerby to a Nautiloid from the Coal-measures, Coalbrookdale, Shropshire, and the description was accompanied by three figures, each representing a different specimen. In 1884 the species was included by Professor Hyatt in his new genus Ephippioceras. In 1891 Dr. A. H. Foord found a new species, Ephippioceras costatum, which was said to be “distinguished from E. clitellarium (to which it is, however, very closely related) by the character of the septa and by the surface ornaments. The septa in E. costatum do not form such an acute lobe upon the periphery as do those of E. clitellarium, and they are also a little wider apart in the former species than they are in the latter. Moreover, E. costatum is provided with prominent transverse costæ, which are strongest upon the sides of the shell where they swell out into heavy folds. These costæ are directed obliquely backwards, and cross the septa at an acute angle, passing across the periphery and forming a shallow sinus in the middle. None of the specimens in the British Museum have the test preserved, so that the ribbing has only been observed upon casts. The costæ are equally well developed upon the body-chamber and upon the septate part of the shell in the adult, but they were either very feeble or altogether absent in the young.” A re-examination of the specimens in the Museum collection shows that the separation of the two forms is quite justifiable.

This species was first described by Sir P. De M. Grey Egerton as Palæoniscus monensis, in 1850, from detached scales from the Coal-measures of Anglesey. Subsequently, Dr. R. H. Traquair proved that the proper position of the fish was in his genus Rhadinichthys. Up to this date only detached scales had been known, but in the paper just mentioned Dr. Traquair described specimens showing many points in the structure of the fish which had been hitherto unknown. In my collection there are many fragmentary remains, collected from the Yorkshire Coal-measures, which show, among other interesting points, the form and ornamentation of many of the bones of the head and shoulder-girdle; while one more nearly perfect specimen shows well the form of the fish and some other points in its anatomy which have not been hitherto described, namely, the relative positions of the dorsal, anal, and ventral fins, the former being very well preserved and perfect.

The district in which these observations have been made is a very suitable one for such experiments, and is situated from 2 to 12 miles from Bacchus Marsh and from 32 to 54 miles west of Melbourne.