Page:Popular Science Monthly Volume 52.djvu/245

Rh upper Jurassic and the Cretaceous and connecting the two; so that there is not in Russia any such gap between these systems, in his view, as is recognized in western Europe. The fauna, however, requires more detailed study before positive results can be assured. He gives much space to this discussion, in which we can not follow him here.

The Jurassic beds below present a close correspondence throughout the whole of central Russia to those of the north and west of France, and no marked differences can be observed.

The Trias and the Permian are here wanting, and the Mesozoic rocks lie directly on the limestones of the "Etage Moscovien" of the middle Carboniferous. Both are fairly rich in fossils, and at the base of the Callovian is a conglomerate in which characteristic Callovian fossils are intermingled with rolled fossils of the underlying Muscovian.

In the journey southward and eastward, from Moscow to Riazan, Penza, Samara, and Oufa, these same rocks occupy the greater part of the way, with much of interesting discussion, until some other features begin to appear as the route approaches the Volga, which it follows from Syzran to Samara. The lower Quaternary bowlder clay begins to disappear and gives place gradually to an upper series of deposits of mingled fluvial and æolian character, the most marked of which are the "loess" and a heavy "terrace clay" of the valleys, with a variety of intermediate types.

At Syzran the general uniformity of the structure is broken by an anticlinal elevation, in a north-to-south course, crossed by an important line of fault, west-northwest and east-southeast. These movements have produced a line of hills, which have deflected the course of the Volga, and are the only examples of the kind in this extensive region. Professor Nikitin places the period of their elevation in the early Tertiary.

At this point a very interesting feature first appears—the occurrence of deposits laid down by the former extension of the Caspian Sea. They are first seen near Syzran, in a baylike portion of the valley of the Syzran River, and thence become more marked in traveling eastward. They are chiefly clayey sands and conglomerates, with rolled pebbles of the underlying Cretaceous rocks. They appear on the divides and higher portions of the banks of the Volga and its affluents, and are evidently older than the "terrace clays" of the upper Quaternary. At many points they contain brackish water shells of late Caspian type. We have here the evidence of the Pleistocene extension of the Caspian waters over the great valley of the Volga as far north as latitude 53°, and even farther.

Crossing the Volga near Samara, the route enters upon a wide