About one quarter of the Island of Jersey is occupied by argillites or fine grits, often of a greenish grey colour referred by French geologists to the “Phyllades de St. Lo.” They are, therefore, if not equivalent to the Lower Cambrian beds of Britain, slightly more ancient.inclose association with these, but according to Prof, de Lapparent, belonging rather to the upper part of the group, occur certain more or less porphyritic rocks, as to the origin of which different opinions have been entertained. M. Nouryinhis useful “Geologie de Jersey ” describes them under the name of “spilites.” While admitting that in many respects they exhibit the characters of an eruptive rock, he concludes, after an elaborate discussion, that they are metamorphosed argillite, the change being primarily due to the “poiphyres pétrosiliceux;” the felspar crystals, however, he thinks, may be attributed to the action of the diorite.