The present notes have accumulated since 1923 during a survey of the solid geology of the region between the western slopes of the Vale of Conway and Moel Wnion, including the district around Tal y Fan mountain, Foel Lwyd and Drosgl, and extending northward to the coast. The glacial deposits and alluvium have been mapped on the 6 in. scale, and a sketch-map is here given (Fig. 1). The areal distribution of the drift is described and an attempt is made to account for some of the glacial and physical features. Some notes are added upon the general character and origin of the Conway Valley.

The precise age of the Millstone Grit of South Wales has been in doubt for some years. Although it has been shown to be of Upper Carboniferous age, it has been uncertain whether the whole of the earliest part of the Upper Carboniferous is represented by deposits in southern Britain. Some part of the Millstone Grit of Pembrokeshire has been regarded, on the basis of its flora, as of Middle Coal Measure or Yorkian age (Goode, 1913, p. 272). Similar conclusions have been reached by Dr. R. Crookall concerning part of the Millstone Grit of Somerset (1925, p. 403). As yet, the flora characteristic of the Lanarkian of northern Britain has not been proved to be present in South Wales and elsewhere in south Britain. On the other hand, it has been argued that the absence of a Lanarkian flora does not necessarily imply an important break in the sequence, since recent work on the lamellibranch fauna of various British coalfields points to the conclusion that the lowest part of the Lower Coal Series of South Wales is of approximately the same age as the Lower Coal Measures of northern England (Davies and Trueman, 1927, p. 253).

Although raised beaches are common enough round the British coasts, the presence of such a beach on the north coast of Scotland merits description, were it only to put on record the occurrence of what is, I believe, the first undoubted example of its kind in this locality.

(1) When the diameter of the umbilicus of an ammonite is plotted against the diameter of the whole shell, or the whorl-thickness plotted against the whorl-height, the curves obtained are very commonly straight lines for the greater part of their courses.

(2) If, as is usually the case, these lines do not pass through the origin, the formula for the ammonite spiral is of the form r + c = eβθ and not r = eβθ.

(3) If the straight lines do not pass through the origin, it is useless to express one dimension as a percentage of the other and compare these percentages in different shells.

(4) There is no way of foreseeing, before the measurements are made, whether the dimensions of a species will plot accurately on a single curve or whether they will show a considerable amount of scatter. If, however, they do fall accurately on a single curve, this fact is an argument for the validity of the species, and the curve is a useful aid in the identification of other specimens.