though relatively in extremely feeble proportions, water is incorporated in the deep masses of the terrestrial crust, in immense absolute quantities, •which are perhaps commensurable with the volume contained in the seas on the surface.
Various physical circumstances, such as the configuration of the soil and the vicinity of rivers or of the sea, have always had a great influence on the grouping and destinies of populations. The presence of particular minerals has had a similar determining influence. The useful metals, coal, and petroleum, have caused important cities to be created and to grow—as Virginia City, Leadville, Eureka, Oil City, and Petrolia, in the United States.
Underground water, a more commonplace substance, which has attracted much less attention, eminently deserves to be considered when we seek for the natural causes that have contributed to the formation of large agglomerations of men. Pliny the Elder remarked that mineral waters had peopled the earth with new cities and Olympus with new gods. Recent excavations in Gallic villages have brought to light vast piscinæ marble monuments, theatres, statues, mosaics, and other unmistakable vestiges of a vanished luxury, as at Nereis, Vichy, Plombières, Bagneres-de-Luchon, and Aix in Provence. Universal celebrity attaches to Baiæ, where every Roman was ambitious to have a country-house, and the ancient splendor of which is attested by ruined temples and palaces. The word "bath" and its equivalents in different languages form the roots of many place-names. Those who lived by the manufacture of salt have necessarily grouped themselves around the marine springs from which their towns have received names embodying the root-form of the word salt or its equivalents—Salins, Chateau-Salins, Salival, Marsal, Salies, Salat, Saleons, Saltz, Saltzbronn, Salzhausen, Salzungen, Salzburg, Hall, Reichenhall, etc.
So populations tend to group themselves around copious fountains of fresh, potable water, where the frequency of the villages is often in striking contrast with the sparsity of the settlements in more arid localities. These contrasts result from the constitution of the soil. The junction of the Jurassic formation with the impermeable clays of the lias on which it rests is marked by a line of frequent springs, around which habitations and villages stand thickly, as in the vicinity of Metz; while the absence of masses of population on the neighboring limestones, where water is reached only at a great depth, is matter of special remark. This abundant and regular water-supply is found under these conditions, and at the same geological level, in many parts of France, England, and Germany, where it always attracts thick populations.
While the cretaceous table-lands of Champagne lack springs, they flow out in abundance at the foot of the cliffs. Many of them bear the generic name of "Somme," because they are the origin or the top of a brook—as Somme-Suippe, Somme-Vesle, Somme-Tourbe, Somme-