Let him remember Lyell's profound remark, that the thickness and extent of sedimentary formations are the result and measure of the degradation which the earth's crust has elsewhere suffered.
Some of these formations, which are represented in England by thin beds, are thousands of feet in thickness on the Continent.
Nor is their rarity surprising, when we remember how large a proportion of the bones of tertiary mammals have been discovered either in caves or in lacustrine deposits; and that not a cave or true lacustrine bed is known belonging to the age of our secondary or palaeozoic formations.
But the imperfection in the geological record mainly results from another and more important cause than any of the foregoing; namely, from the several formations being separated from each other by wide intervals of time.
But we can, I think, see why the geological formations of each region are almost invariably intermittent; that is, have not followed each other in close sequence.
I am convinced that all our ancient formations, which are rich in fossils, have thus been formed during subsidence.
Consequently formations rich in fossils and sufficiently thick and extensive to resist subsequent degradation, may have been formed over wide spaces during periods of subsidence, but only where the supply of sediment was sufficient to keep the sea shallow and to embed and preserve the remains before they had time to decay.
Le ministere a pris l'initiative de publier des textes reglementaires au cours du premier semestre de cette annee afin d'encourager les entreprises a adherer au systeme de la formation
continue et a accelerer les mesures de couverture des depenses investies dans la formation
continue, a-t-elle declare au correspondant de l'agence TAP dans la region, lors de l'inauguration du complexe regional de la formation
continue et de la promotion professionnelle a Sousse.