The region lying along the southern border of the Canadian Shield, the St. Lawrence basin, to which by far the greater part of the field work so far performed in this vast area has been confined, is divided into four geographically separate sub-provinces, in each of which the succession of formations is so different that few positive correlations of either formations or unconformities in different sub-provinces can be made. It is probable, however, that all geologists familiar with this region are agreed that there is a palaeoplain at the base of the Huronian that originally at least extended over the southern part of the Canadian Shield. If the existence of this palaeoplain be assumed as established then there are two major problems in Pre-Cambrian classification in this region that remain unsolved: (1) What is the position of the pre-Huronian palaeoplain in the succession of formations present in the sub-province north-west of Lake Superior and in the Grenville sub-province? and (2) is there a second erosion plain within the pre-Huronian complex, and, if so, can it be used satisfactorily for the classification of the pre-Huronian into two major divisions equivalent in rank to the Huronian?

The purpose of this paper has been to point out (1) that there is no present agreement regarding the solution of either of these problems; (2) that the existence of a widespread unconformity within the pre-Huronian complex of the St. Lawrence province is, as yet, only a hypothesis, and (3) that there are only two logical courses to be followed in the classification of the Pre-Cambrian formations of the Canadian Shield, either to adopt the dual classification or to use it tentatively in the manner indicated in the accompanying table, until the existence of the second widespread unconformity is established or disproved. It may be suggested, however, that since considerable difficulty is being encountered in applying the dual classification even within the St. Lawrence province, it may be more practical to adopt the dual classification for the major divisions of the Pre-Cambrian notwithstanding the possible presence of an unconformity within the pre-Huronian complex.

In conclusion the writer wishes to express his indebtedness to his colleagues of the Geological Survey of Canada, W. H. Collins, F. J. Alcock, T. L. Tanton, and J. F. Wright, for criticism of the columns in the table of formations having reference to the different sub-provinces with which they are especially familiar.

A case is described of rhythmic banding by iron oxide in a rhyolitic tuff. The fine-grained tuff has acted as a medium for the production of Liesegang rings, the irregularity in the rings being ascribed to minute variations in the texture of the rock, naturally less homogeneous than a gel.

The foregoing sketch brings out marked resemblances in the geological features of eastern and southern England on the one hand, and the neighbouring parts of the continent on the other. In both areas we find an old plateau of pre-Devonian rocks, against which Devonian and Carboniferous rocks are violently thrust from the south by Armorican and Variscan folds, giving rise to highly complex coal-basins in Belgium, France and Somerset, a type of structure possibly to be encountered in the future in Kent. In Belgium this plateau sinks to the north-east under the Campine coalfield, while in England its north-west margin is complicated by the incidence of posthumous folds of Charnian strike.

In eastern England, east of the Charnwood line, there is evidence for the existence of Professor Kendall's Willoughby axis, with north-west strike; between this and the Charnwood line there are indications of similar parallel buried trend-lines in the folding and faulting of the visible Yorks-Derby-Notts coalfield, and also, as suggested by Professor Fearnsides, in the general shape of this basin.

Further to the north, however, the general line of the Cleveland and Market Weighton axes is not Charnian, being about west 5° north. The Market Weighton axis, which is of Charnian type, with many repeated movements, does not form the boundary of the coalfield; this is in fact constituted by the southern flank of the broad Cleveland uplift, which is of Wealden type; an anticline superposed on an earlier sinking area.

Beds of shale, sandstone and conglomerate containing Upper Cretaceous fossils occur at several places in Jamaica, and in every instance that I know of they are found to be more or less in close association with Rudist limestones. They generally occur below the limestones with Rudistae but in at least one locality, that at St. Ann's Great River, fossiliferous shales occur immediately above and also a considerable distance, 1,000 feet or so, below a bed of Rudist limestone.