Memoranda on Tours and Touraine / Including remarks on the climate with a sketch of the Botany And Geology of the Province also on the Wines and Mineral Waters of France

by J. H. Holdsworth

Those «medallions of Nature,» the fossils which they contain not only furnishing us with a chronological knowledge of the progressive formation of the Earth's crust, but recording in language the most intelligible, what were the peculiar states, and characteristics of animal and vegetable existences at the distinct, and distant epochs of the World.

By the aid of these silent but eloquent intelligencers, we discover that the strata which now constitute the table lands of Touraine, were among the last, in the whole geological series, that emerged from the waves of the Ocean. That, that grand instrument of transposition and renovation, has in a general sense, ever since been restrained within its mighty confines. And that at the time its waters last prevailed over these regions now high and dry, many of the types of living testacea, etc. were become identical with those of existing species.

Touraine, or the department of Indre-et-Loire, may be said to be the grand repository of the tertiary formations of central France. It constitutes the southern divisions of the great Paris basin, formed by a vast depression in the chalk, and which is about 180 miles long and 90 miles broad. This cretaceous or chalk basin terminates to the south a short distance from Poitiers, where the oolites and certain other formations older than the chalk, crop out from beneath it, and thence forward, principally constitute the formations of the more southern departments of the kingdom: and occasionally extend to the summits of the gigantic Pyrénées.

The long range of rocky precipices often constituting rather lofty escarpments, along the northern borders of the valley of the Loire, are a portion of the extensive cretaceous formations which surround Paris. In the vicinity of Tours and many other places where its strata are alike exposed to view, many beautiful specimens of some of its characteristic fossils may be readily obtained; this formation here also frequently contains its usual layers of flint, and which often assumes the exact form of the zoophytes, and other organic structures, into which it has percolated.

But in this locality, as also in many instances in the chalk region south of Angoulême, the mineralogical character of the formation is often completely altered, chiefly appearing as a fine white calcareous sandstone, occasionally passing into a compact siliceous limestone, similar to the calcaire siliceux of the superior freshwater limestone, but for the most part destitute of the small sinuous cavities the latter commonly contains.

This calcareous sandstone is directly succeeded, in ascending order, by the most extensive surface deposit of Touraine, termed by the French geologist, argile et poudinge; a rather thick argillaceous deposit, in which flint boulders are sometimes thickly embedded, and on which reposes the calc d'eau douce or freshwater limestone, both formations belonging to the uppermost subdivision of the Parisian tertiary strata, or newer Pliocene deposits.

Immediately above the freshwater limestone just named, a series of isolated masses occur, consisting of marine sand and marl, the whole rarely exceeding fifty feet in thickness, and containing for the most part a different and immense assemblage of fossils. This tertiary formation which is provincially termed faluns, (broken shells) is considered to belong to a period intermediate between that of the Parisian and subapennine strata, and to assimulate in age to the crag formation of England, which belongs to the Miocene or middle Tertiary.

M^r Lyell who has closely examined the faluns[D], says that most of the shells they contain do not depart from the Mediterranean type, although a few would seem to indicate a tropical climate, among these may be mentioned some large species of the genera conus, terebra, rynula, tasciolaria, cerithium and cardita.

The species he considers for the most part marine, but that a few of them belong to land and fluviatile genera. Among the former, helix turonensis (faluns Touraine) is the most abundant.

Remains of terrestrial quadrupeds are here and there intermixed, belonging to the genera mastodon, rhinoceros, hyppopotamus, deer and others, and these are accompanied by cetacea, such as the lamantine, morse, sea calf, and dolphin, all of extinct species.