The chief features exhibited by the heavy mineral residues from the various formations will now be summarized, but it is difficult to show, by tabulating or otherwise, the differences or resemblances between residues, although such may be quite obvious to the investigator. This is because the differences consist of a sum total of variations in size, shape, colour, and frequency of the mineralscontained in the residues under examination, and it is scarcely possible to indicate such differences in writing, without frequent repetition of words, there by involving a loss in clarity of expression, or if tables be employed, without losing sight of other connected data.

A geological survey of the Pre-Cambrian area of South-Western Lleyn and of some of the Ordovician country to the east of it was made by the present writer between the years 1909 and 1912. An account of the geology of Bardsey Island was published in 1913, but ten years' absence abroad has delayed the description of the rocks of the adjacent mainland. A further absence from Europe will cause additional delay in the presentment of a full account of the district, and it seems desirable that some of the more important results of the survey of this tract of ground should now be placed on record.

In 1907 Mr. E. H. Cunningham Craig's Report on the ‘Metamorphic Rocks of Trinidad’ was published, containing a general description of the structure of and the beds composing the Northern Range of the Island, and this note is accordingly intended merely to call attention to the petrographical characters of some of these altered sediments included in the Caribbian Series of Wall and Sawkins, and by far the oldest rocks in the island.