and Jurassic periods and continued to be a sediment receiving basin since. In between the zone of Alpine orogeny and North Sea Basin subsidence, highlands resulting from an earlier orogeny (Variscan) remained, such as the Ardennes, Eifel and Vosges. From the Eocene onward, the ongoing Alpine orogeny caused a north–south rift system to develop in this zone. The main elements of this rift are the Upper Rhine Graben, in southwest Germany and eastern France and the Lower Rhine Embayment, in northwest Germany and the southeastern Netherlands. By the time of the Miocene, a river system had developed in the Upper Rhine Graben, that continued northward and is considered the first Rhine river. At that time, it did not yet carry discharge from the Alps; instead, the watersheds of the Rhone and Danube drained the northern flanks of the Alps. Stream capture The watershed of the Rhine reaches into the Alps today, but it did not start out that way. In the Miocene period, the watershed of the Rhine reached south, only to the Eifel and Westerwald hills, about north of the Alps. The Rhine then had the Sieg as a tributary, but not yet the Moselle. The northern Alps were then drained by the Danube. Through stream capture, the Rhine extended its watershed southward. By the Pliocene period, the Rhine had captured streams down to the Vosges Mountains, including the Main and the Neckar. The northern Alps were then drained by the Rhone. By the early Pleistocene period, the Rhine had captured most of its current Alpine watershed from the Rhône, including the Aare. Since that time, the Rhine has added the watershed above Lake Constance (Vorderrhein, Hinterrhein, Alpenrhein; captured from the Rhône), the upper reaches of the Main, beyond Schweinfurt and the Moselle in the Vosges Mountains, captured during the Saale Ice-age from the Meuse, to its watershed. Around 2.5 million years ago (ending 11,600 years ago) the Ice Ages began. Since approximately 600,000 years ago, six major glacial periods have occurred, in which sea level dropped as much as and much of the continental margins were exposed. In the Early Pleistocene, the Rhine followed a course to the northwest, through the present North Sea. During the so-called Anglian glaciation (~450,000 yr BP, marine oxygen isotope stage 12), the northern part of the present North Sea was blocked by the ice and a large lake developed, that overflowed through