While working at the Lower Liassic Ammonites of the Sowerby Collection, preserved in the British Museum (Nat. Hist.), the author happened to come upon one of the paratypes of Ammonites Greenoughi, J. Sowerby, which could be recognized at once as being allied to Schlotheimia Charmassei, d'Orbigny, sp. On going into the matter in greater detail it was found that the suspicions of some Ammonite workers regarding the misinterpretation of the species by most previous authors were, indeed, well founded. Quenstedt, for example, had stated that Wright, having found Sowerby's type very much disfigured by decomposition of pyrites, substituted for it a gigantic specimen of a diameter of 440 mm., “which, however, looks different again.” Pompeckj again stated that the gigantic specimen drawn by Wright, as well as his description defined the species in a not very precise manner, and that, therefore, it was not certain that the specimen agreed with Sowerby's original.

So far, the source of the heat lost from the earth has been assigned only to the disintegration of the radio-active elements. Besides this, heat is liberated near the surface by the processes of weathering. The decomposition of one gram of average rock is accompanied by the generation of about 120 calories. Owing to its extreme slowness, this source of heat generation is of practically no importance except locally, where for a time it may succeed in appreciably steepening the temperature gradient. The heat liberated by weathering is probably balanced by the absorption of heat at greater depths, which is involved in the processes of metamorphism. Of much greater importance is the question whether the earth can still be regarded as possessing an ancient heritage of heat dependent on its origin.

Scattered throughout the Palæozoic rocks there are frequently found certain fossils, in most cases represented by single detached plates, which have been ascribed by various authors to the sub-class Cirripedia. Thus we have fossils described under the names Balanus, Cirripodites, Lepidocoleus, Plumulites, Pollicipes, Protobalanus, Scalpellum, Stenotheca, Strobilepas, and Turrilepas, but in the case of Balanus, Pollicipes, and Sealpellum, the reference to those recent genera is quite unsupported by the structure of the fossils.

All the phenomena hitherto noticed have been worked out for the case of rocks altered in situ, but they also take place in the products of transport resulting from the demolition of laterites in situ.

On approaching the problem of the origin of laterite, the first thought that strikes one is that there is an apparently fundamental difference between the modes of decomposition of aluminous silicates in temperate and in tropical regions. For in temperate regions the end product is a clay, in which the original aluminous silicates are represented by hydrated aluminium silicates approximating in composition to kaolinite, whilst in the tropics the end product is laterite, in which the original aluminous silicate is represented by a mixture of hydrated aluminium oxides. The two processes may be expressed by the following chemical equations:—

Professor Lacroix finally states his views on the age of various sorts of laterite, regarding it as probable that all the phenomena considered in his memoir are still in a state of active evolution, although no direct observation of this can be made, except in the case of ferruginous concretionary action at the surface of the cuirass. But he gives evidence to show that the process of lateritization must be a slow one. There are laterites of at least two ages, as proved by the eroded cliffs of ‘fossil laterite’ contrasted with the latérite d'alluvions of the valleys, these two types corresponding in position to our Indian high-level laterite and low-level laterite. He finally concludes that (p. 351)—