To the earthquake that ruined Lisbon on November 1, 1755, we may trace the great interest in the study of earthquakes which marks the middle of the eighteenth century, though valuable accounts of previous earthquakes had already appeared in the pages of the Philosophical Transactions. During the following year the Royal Society paid the same close attention to this earthquake that it did more than a century later to those of the eruption of Krakatoa. In 1757 an anonymous editor published The History and Philosophy of Earthquakes, in which he gave abstracts of ten memoirs by the “best writers on the subject”—Hooke, Woodward, Buffon, and Stukeley among them—followed by a summary of the observations on the Lisbon earthquake that had been communicated to the Royal Society. These are the principal sources on which Michell depended when he wrote his memoir on the cause and phenomena of earthquakes.

The Term “Cycle of Sedimentation” or “Cycle of Deposition” is not nearly so familiar in England as it is on the Continent. Whilst the teaching of the general principles forms part of most courses in geology, the application of these principles to actual successions in this country has been somewhat neglected. Attention has recently been drawn to the seasonal or rhythmic changes seen in some sediments, and to avoid confusion it is desirable to outline what is meant by the expression “Cycle of Sedimentation”.

The age of a concretion, relative to that of the parent-rock, must be either:—

1. Contemporaneous.—The concretion grew on the sea-floor at the same time, and at about the same rate, as the surrounding deposit was laid down.

2. Penecontemporaneous.—The concretion segregated more or less close to the surface of recently deposited sediment.

3. Subsequent.—The concretion formed after deposition had finished, and after the strata had largely consolidated, but, perhaps, before cementation had taken place to any noteworthy extent.

Occurrence of the Oil.—The oilfield of Jaba and those of Rawalpindi and Fatehjang are identical from the stratigraphical point of view. At Jaba, too, the oil is to be found in the contact zone between the Nummulitic limestone and the younger gypsiferous clays of the Upper Nummulitic. These gypsiferous clays represent a bed well adapted to favour the accumulation of oil, wherever they cover the limestone at a moderate inclination. The oil issues only from the limestone, but the cellular limestone, too, may be oil-bearing in depth. It may be pointed out that cellular limestones of the same character accompany the oil-shows at Gunda, the main oil-spring in the neighbourhood of Fatehjang.

In the Oolitic rocks of the Cotteswold Hills fissures are of frequent occurrence. Noticeable phenomena are that when snow or hoar frost is on the ground it is usually melted or not deposited along the lines of these fissures and that air is usually continuously expelled from them.