In his master's steps he trod . . . Heat was in the very sod"-Traditional SummaryFifteen measurements of the heat flow through the ocean floor have been made in the Atlantic and one in the Mediterranean. One measurement in the central valley of the Mid-Atlantic Ridge gives a heat flow of 6.5 pcal/cmZs. Similar very high values have been found by others on the crest of the East Pacific Rise. The possibility that these high values represent the rising limb of a convection current is discussed. The mean of the remaining fifteen values and of five from a previous investigation, give a mean heat flow of I -06 & 0.055 pcal/cm2 s which is very close to the mean for all measurements in the Pacific excluding those on the East Pacific Rise.The equipment has been modified so that the temperature gradients in the whole probe and in its lower half can be determined separately.The lower half gives a value 8.8 per cent above that for the whole probe, the reason for this is not known.The thermal resistivity of ocean sediment, R, is found to be a linear function of the water content, w (in per cent water of the wet weight). At the temperature of the ocean floor the relation is R(cms degC/cal) = (168i-14)+(6.78+0-31)~.

The main feature of the gravity field of Devon and Cornwall is a belt of large negative Bouguer anomalies which follows the line of the granite outcrops. These low anomalies are shown to originate from a shallow structure and are interpreted as being caused by the relatively low density of the granite itself. They indicate that the exposed granites are cupolas on a single elongated batholith which reaches a depth of at least 8 and possibly 20 km. The magnetic anomalies between Dartmoor and Bodmin Moor support the idea of interconnexion. A more detailed interpretation of the gravity anomalies shows that the contacts between the granite and the enveloping country rocks generally slope outwards. For Dartmoor, at least, the base of the batholith seems to be deeper in the south. A mechanism of emplacement combining forcible intrusion with stoping, in which the magma rose in the south, is consistent with the shape suggested. In marked contrast to the granites of the mainland and Scilly Isles there is only a small drop in the Bouguer anomalies over the Lundy granite, suggesting a laccolithic space form. The present high ground corresponding with the granite exposures of the mainland is shown to be isostatically compensated, or even overcompensated, by mass deficiencies implied by the negative anomalies. As the anomalies seem to be caused by the low density of the granite the compensation is almost certainly caused by the relatively low density of the batholith itself. The distribution of the compensating mass deficiency thus suggested is in closest agreement with Pratt’s hypothesis. The depth of compensation is unusually low at about 1 o or 15 km. There is a marked southward increase of the Bouguer anomalies over the Start and Lizard peninsulas which is thought to be related to the presence of a thrust affecting these regions. Similarly, the northward decrease of the gravity anomalies across Exmoor is attributed to a major overthrust beneath which a great thickness of Carboniferous and Devonian rocks is likely to be present. It is thus possible that Coal Measures are to be found at no great depth beneath the Devonian rocks of the Dunster-Minehead region. Over the Culm synclinorium three east-west ridges of higher Bouguer anomalies are superimposed on a westerly regional gradient and are shown to be of shallow origin. The high magnetic anomalies in this area suggest the presence of magnetic rocks extending to a considerable depth. A smaller gravity ‘low’ coincides with the Crediton trough of Permo—Triassic rocks. A detailed traverse at North Tawton indicates that the trough here is V-shaped and has a maximum depth of 340 m. Depth estimates have also been obtained for the Tertiary lacustrine deposits of Bovey Tracey and at Petrockstow.

In his master's steps he trod . . . Heat was in the very sod"-Traditional SummaryFifteen measurements of the heat flow through the ocean floor have been made in the Atlantic and one in the Mediterranean. One measurement in the central valley of the Mid-Atlantic Ridge gives a heat flow of 6.5 pcal/cmZs. Similar very high values have been found by others on the crest of the East Pacific Rise. The possibility that these high values represent the rising limb of a convection current is discussed. The mean of the remaining fifteen values and of five from a previous investigation, give a mean heat flow of I -06 & 0.055 pcal/cm2 s which is very close to the mean for all measurements in the Pacific excluding those on the East Pacific Rise.The equipment has been modified so that the temperature gradients in the whole probe and in its lower half can be determined separately.The lower half gives a value 8.8 per cent above that for the whole probe, the reason for this is not known.The thermal resistivity of ocean sediment, R, is found to be a linear function of the water content, w (in per cent water of the wet weight). At the temperature of the ocean floor the relation is R(cms degC/cal) = (168i-14)+(6.78+0-31)~.

Summary On the basis of the measured seismic velocities, the layering found at 25 seismic stations in the area of the Western Approaches of the English Channel is divided into four classes which are respectively correlated with semi-consolidated Cretaceo-Tertiary sediments, the New Red system, the Palaeozoic system, and a metamorphic basement. The last of these appears to form a long, deep trough. The Palaeozoic floor is depressed in a trough of somewhat variable depth, bounded on the north by an outcrop of the metamorphic basement which is possibly a westward extension of the upthrust Lizard-Start metamorphic belt. Contour maps of the layering are produced.

The first surveys of global magnetic intensity, and especially the demonstration of its variation with latitude, are commonly credited (for example, Chapman, [1967]) to Alexander Von Humboldt, who played a major role in developing geomagnetism in the late 18th and 19th centuries. Von Humboldt made intensity measurements in South America from 1798–1803 and later encouraged the establishment of a global magnetic observatory network (see, for example, Malin and Barraclough, [1991]). However, as pointed out by Sabine [1838] in a review of intensity measurements to that time, the earliest surviving survey of global magnetic intensity, showing it to strengthen away from the equator both north and south, was made by Elisabeth Paul Edouard De Rossel during the 1791–1794 expedition of Bruny D'Entrecasteaux. Even earlier measurements seem certain to have been made by the scientist Robert de Paul, chevalier de Lamanon (always referred to as Lamanon) of the La Pérouse expedition [Milet‐Mureau, 1799], but any records are evidently lost. Lamanon died when the La Pérouse expedition was in Samoa in 1797, and both ships of that expedition were wrecked on the island of Vanikoro, presumably in 1788 [Marchant, 1967; Spate, 1988]. All such measurements were of relative magnetic intensity until a method for the determination of absolute intensity was invented by Gauss in 1832. For a recent discussion of this latter topic, see Jackson [1992].