In 1911 Dr. W. B. Wright briefly described the felspathized quartzite blocks in the hornblendite of Port Easdale, Kiloran Bay, Colonsay, Hebrides. He showed that the exposures provide a conclusive demonstration that the action of hornblendite magma on quartzite xenoliths was to convert them to alkali-felspar and quartz, so that in the final stage ‘one can recognize in numerous angular and rounded patches of felspathic material, without visible xenolithic core, the ghosts of former masses of quartzite’.

The occurrence in basic lavas of quartz xenocrysts and xenoliths and the various types of reaction phenomena which they exhibit have been well described by Lacroix (1893, pp. 17-48). The modified quartz is often surrounded by a zone of pyroxene granules or prisms and on the inner side of this zone the quartz may be replaced by glass, both peripherally and through an anastomosing system of vein-like channels. The glass may be clear or charged with gas inclusions; some examples contain minute quartz-pseudomorphs after tridymite, while in others microliths of alkali-felspar occur. In the basanitoid of Hirzstein, Hesse, nepheline occurs around quartz in place of the usual vitreous shell (Fromm, 1891, pp. 58, 65, and 70). Despite these observations, it seems to have been tacitly supposed that the glass is a more or less hydrous variety of vitreous silica.

In Haüy's original definition of eclogite, the presence of kyanite as an accessory constituent was recognized, and it is apparent that he was familiar with examples from the Sau Alps and Styria. The best known of eclogites—those of the Bavarian Fichtelgebirge (e.g. Silberbach, Weissenstein, and Eppenreuth)—contain significant kyanite interspersed among the omphacite grains or associated with accessory quartz and muscovite in the rocks. Of these rocks rather extended descriptions have been published. Analyses of the minerals and the rocks themselves belong to an early date and do not reach the standard of modern analyses. Later, Drill (1902) published a systematic account of these Bavarian eclogites and has added an analysis of an eelogite with kyanite from Unterpferdt near Silberbach and an analysis of a garnet from a Silberbach eclogite.

Rocks composed mainly of the hydrated ferrous silicate greenalite are of very restricted geological and geographical distribution and, up to the present, have been recognized only from certain of the pre-Cambrian sedimentary iron-bearing formations of the Lake Superior region. It is of interest, therefore, to record an additional occurrence, not only from another region but from a later geological system.