The Geological History of the Thames is still the subject of conflicting hypotheses. Mr. F. W. Harmer (1907) has drawn a very interesting parallel between the basin of the Middle Thames around Oxford and the Vale of Pickering in Yorkshire. The latter, as is well known from Professor Kendall's paper (1902), was occupied by a glacial lake which was due to the Derwent River having had its outlet to the sea south of Scarborough closed by a dam of ice; the water rose in this lake until it overflowed at a gap near Malton; the river thus formed cut a gorge through which the drainage from the Vale of Pickering flows south-westward into the Yorkshire Ouse, and reaches the sea through the Humber. According to Mr. Harmer the Upper Thames originally discharged north-eastward through the Fens into the Wash; this outlet was blocked by the ice; the waters of the Upper Thames collected as a lake, which was discharged by overflow channels cut through the Chiltern Hills, and as the lake-level fell the discharge was maintained only through the Goring Gap at the south-western end of the Chiltern Hills. This view advances a different explanation of the Chiltern wind gaps than that advocated in a paper in 1894, and is opposed to the theory of the evolution of English rivers adopted by Professor W. M. Davis in 1895.

From the foregoing analyses there is little doubt that the rock is a hornblende-quartz-keratophyre. The term porphyrite, however, has been adopted in the mapping for convenience. It is worthy of note that a very similar rock, though greenish in colour, has been already described from Kanowna by the writer. In the latter, silica amounted to more than 71 per cent, while soda reached 7.85 per cent; potash was again absent.

12237, G.M.L. 4458 E., Hyman North.

The physical history of sedimentary rocks is written in charácters which sometimes baffle the skill of geologists to interpret. This may be because geologists are prone to devote too little time to the study of rocks in the making, and too much to the finished products of sedimentation. It is well to remember that the most unpromising pool or bit of lake shore may hold the key to the most perplexing of these hieroglyphics.

A brief review of the history of the various attempts to explain certain curious impressions found on the Niagara dolomites of Western New York will illustrate the need of closer observation and study of some of the phenomena of our ponds and lakes resulting from the interaction of wind and water.

The Cover-plates of the radial grooves are preserved here and there in specimen, notably over the oral centre (Pl. X, Figs. 1, 2, 5, 7, 8), but in B they are preserved over the whole of the grooves and the mouth, though pressed down on to the floor of the grooves and into the peristome (Pl. XI, Fig. 1). Cover-plates are also present in the British Museum specimens, and are almost complete in E 16054.

Each cover-plate corresponds in position with a floor-plate; so that, like the floor-plates, the cover-plates form a double series of alternating plates meeting in a zigzag median suture. The almost straight or slightly rounded outer margin of each cover-plate fits into a bevelled facet just within the rounded edge of the radial groove where the floor-plate begins its downward slope (Pl. X, Figs. 5, 7). This feature is well shown in specimen B, and there the floor-plate also shows, on each, side of the facet, and distinct from the peripodium, a slight depression, possibly for the insertion of a muscle or ligament, or possibly for the reception of the accessory cover-plate shortly to be described.

Early in the year 1913 the Copenhagen Museum of Mineralogy and Geology issued a report upon a most interesting deep boring in the Chalk at Gröndal, just outside Copenhagen. The results are so striking in respect to the thickness of chalk passed through that it appears desirable to bring them before the notice of English geologists. The estimates of the thickness of the English Chalk which are considered to be the most reliable are those given by Rowe from measurements of the various zones in the Isle of Wight and Dorset. These are approximately as follows:—