There are unfortunately few graptolites that have retained their original chitinous periderm;when these are preserved in rocks of suitable composition they may be isolated from the matrix, and having escaped distortion, may then be studied more or less in their original condition, and much of our knowledge concerning the structure shown by this group of fossils has, in recent years, been derived from such specimens;these, since they are preserved more or less in relief, differ greatly in appearance from the film-like fossils which are of far commoner occurrence, and which can rarely be taken at their face value, but require some degree of interpretation before identification is possible. Lapworth and Nicholson both recognized this, and it is much to be deplored that modern palaeontologists too often ignore this necessity for interpretation and take graptolites at their face value, with the result that specimens that are only views of well-known species are described as new species or varieties, and the literature of the subject is again being burdened with a number of names of no scientific value or significance.

In all modern textbooks of stratigraphy the fundamental basis of the classification is the division of the rocks of the earth's crust into four great groups, each of which carries a variety of names but all agree in a hard and fast demarcation of the stratigraphical column. Each of these major groups comprises a certain number of systems, as to whose definition there is on the whole general agreement.

The subject of stratigraphical classification and nomenclature has given rise to much controversy in the literature.

Some eight or nine tracts are now recognized. At Bangor there are two, and an isolated one at Carnarvon;the rest are in the Tregarth country. On the older one-inch maps, all of this was coloured as Cambrian, but during the “25-inch” survey, the greater part of it had to be transferred to Arvonian, reducing the Cambrian to a group of outliers.

Through the courtesy of the Ministry of Information and of the military authorities in Naples, the Department of Mineralogy and Petrology, Cambridge, have received samples of the latest ejectamenta from Vesuvius—lava, probably from the neigbourhood of S. Sebastiano, and ashes and lapillae from Salerno.

As a result of a recent controversy not itself directly palaeontological, the graptolite zones of the Ludlow have come in for much implied criticism (e.g. Jones, 1937, p. 280). Unless this criticism is faced, the well-known zonal work of E. M. R. Wood (1900) will sooner or later fall into disrepute, and a considerable volume of stratigraphical work on the Upper Silurian of North Wales will likewise share this fate.