When such minerals as mica, pyroxene, nepheline, fluorite, and hematite are mentioned to us, we can hardly avoid associating their genesis with very high temperatures, and if amphibole be added we are equally bound to imagine also the existence of high pressure. So deeply rooted is this, I might almost say, superstition that few petrographers, when they find such minerals lining the fissures or cavities in rocks, fail to immediately conclude that great heat, and sometimes pressure, is indicated by such an occurrence. No doubt that in the vast majority of cases they would be right, yet I hope to show in these notes that such minerals have occasionally been produced under little or no pressure at a temperature so low as to be insufficient to carbonize or even discolour the organic matter of bone, that is at a temperature considerably below that of an ordinary baking oven.

After a recent visit to Trinidad I am led to add my testimony to that of the numerous observers, who for more than a hundred years have written concerning this remarkable phenomenon.

Over the area in question the total thickness of the Chalk (where it can be measured from top to bottom, or nearly so) varies from 623 feet at Streatham to 1146 feet at Norwich, and in the latter case the topmost beds are absent; so that the full thickness, in some parts of Norfolk, may be 1200 feet or more. This figure, however, is exceptional, the nearest to it recorded being 890 at Harwich [this should probably be 895, the Glauconitic basal bed having been called Upper Greensand]. At East Horsley, in Surrey, a thickness of 817 feet has been proved, but generally speaking we find less, and over a large area 700 feet is not reached. It seems that the Chalk thins toward London (where 650 feet may be taken as about the usual thickness), not only from north and south but also from east and west. [It may be well to add the thicknesses proved by other borings outside London. These are as follows, where the borings have passed through the whole formation, from the overlying Tertiary beds to the underlying Upper Greensand or Gault:—Loughton 651 feet, Richmond 670, Cheshunt 681, Chatham and the neighbourhood 680–684, and Winkfield, near Windsor, 725. In sundry places where the topmost beds are missing we have the following:—Bushey (Herts) 686, Chartham (Kent) 735, and Coombs (Suffolk) 817, which last-mentioned should probably be over 820, for the same reason as given above, for increase at Harwich.]

One of the contact-rocks from Shap, which I collected a few years ago, has always presented some points of special interest; and in view of a recent careful re-examination of it, microscopical and chemical, I think a few remarks upon it may not be out of place.

About two and a half miles east of Kidderminster, in North Worcestershire, is a wooded hill, marked and named Bissell Gorse on the original one-inch Ordnance Map [1831], Sheet 54, N.W. It is now on the six-inch Map [1882], Sheets Worcestershire VIII, S.E. and IX, S.W., named Bissell Wood. The hill lies just half-way between the villages of Stone and Churchill.

Between Dover and Folkestone there are certain deposits of ferruginous sandstone or sandy ironstone, well known to geologists, and somewhat doubtfully referred to some portion of the crag. They may be the equivalents of the Lenham Beds, which are assumed to be the lower part of the Coralline crag, and which have been correlated with the Diestian Beds of Belgium. This view is entertained by Prof. Prestwich, Mr. Clement Reid, and others, and is based upon palæontological evidence (chiefly from Lenham, near Maidstone), from which locality Mr. Reid procured casts of the following fossils:

Since the appointment of the Sub-Committee upon Glacier Observations sufficient time has not yet elapsed for many exact data to have come to hand, with one very brilliant exception— that of New Zealand.

Glauconite may be described as essentially a hydrous silicate of iron and potash, but of very variable composition, and generally containing varying proportions of other bodies, such as alumina, lime, and magnesia. It is found at different horizons in the whole geological series of rocks from the Cambrian up to the most recent Tertiary layers, and, indeed, is particularly interesting in being one of the very few silicates which are in actual process of formation on the sea-bed at the present time. The physical characteristics of glauconite grains are practically the same throughout the series, the normal colour being dark green, but sometimes being yellowish, greyish, or even almost red. These variations of colour, however, mean at least the commencement of decomposition. The size of the grains is usually about one millimetre in diameter, and although much larger masses are sometimes found these are merely agglomerations of the smaller grains. Under the microscope the grains appear quite homogeneous unless some foreign body is enclosed, or, as sometimes occurs, the commencement of decomposition gives a more or less zonary appearance to them.