Publisher's Synopsis
From the INTRODUCTION.
The Gault is a deposit of blue, grey, and sometimes of reddish clays and marls, which are met with in the middle of the Cretaceous strata above the topmost beds of the Upper Neocomian formation viz. the zone of "Ammonites mammillaris," and is by the majority of French geologists looked upon as Gault; but English geologists differ as to this division, the reason for which will be given further on in this work.
The lower beds of the Gault in Kent, Sussex, Surrey, Cambridge, &c. consist of stiff blue clay; the Upper Gault is greyer and more marly. In Norfolk and parts of Yorkshire, the representative of the Gault consists of red marly clays, and in parts of East Sussex it sometimes consists of brown, red, and yellowish clays passing into black shales. In many parts of France it partakes of a yellow and greenish sandy nature.
In some places its soil is known agriculturally as the "black land."
The term "Gault" appears to have been used in Cambridgeshire and Lincolnshire alike for all dark-coloured clays, whether Kinimeridge, Oxford, or Gault.
It is recorded that William Smith (the father of English Geology) was the first to give, this name to the formation, which was originally in use amongst the workmen of Cambridgeshire. It was variously spelt "galt," "golt," and "gault" and has been at times described as Folkestone marl and blue chalk marl.
In the following pages it is the author's intention to describe the Gault, and give some idea of its geographical extension in England and France, and to show by correlation the various equivalents of the Gault of Folkestone, and to append lists of fossils.
The clays of the Gault originated in the trituration of the neighbouring lands, which in England, on the west side of the Anglo-Parisian basin, were for the most part composed of Jurassic or Neocomian rocks; on the north-east of the basin, "i.e," the Ardennes, the sea laved Primary rocks; whilst on the east and south-west of the basin the waves beat against cliffs composed of granites, porphyries, Jurassic and Neocomian rocks.
It is in this manner that the composition of the Gault varies in different localities, according to the nature of the adjacent lands at the time of its deposition; and as these different conditions obtained, so did the fauna vary in the several localities.
