Recently Mr. A. Stuart (1927, PP. 545–57) has published an account of the variation in a large number of specimens of Volutospina spinosa from the Calcaire Grossier of Grignon. In his study of that group he emphasized the variation in the ontogeny of the individual, and suggested the importance of such studies in relation to the more philosophical aspects of biology and in relation to the application of ontogenetic evidence to the problem of classification. The group studied by Mr. Stuart was one in which the latitude of variation in any character was particularly small.

The geological succession and structure of the district are briefly summarized. Evidence of stress conditions becomes increasingly abundant as one passes from south to north towards the boundary of the Carboniferous.

The thermal alteration due to the Bodmin Moor granite is definitely delimited by tracing the outer limit of spotting in normal pelitic sediments.

Petrographical study of phyllites from outside this limit shows considerable mineralogical reconstruction in the sediments, with crystallization of white mica, chlorite and chloritoid; in some instances garnet is developed. The distribution of these types shows no relationship to the granite outcrop, but accords with the main structural features of the area.

Analogous changes are prominent in the igneous horizons, with the formation of schists of the general type of prasinite.

Within the aureole thermal effects can be traced superposed on the earlier dynamic changes.

From these lines of inquiry it is concluded that many of the changes in the phyllites, notably the formation of porphyroblastic white mica, chlorite and chloritoid, hitherto ascribed with greater or less finality to the action of the granite, are due to an earlier dynamic metamorphism.