Similar testimony is found in the great scarcity of cavern and shelter stations in Acheulean times in every part of western Europe; yet occasionally the tribes repaired to the vicinity of sheltering cliffs, as along the Vézère. In some scattered localities they sought the caverns, as at Krapina, in Croatia, at Spy, on the Meuse in Belgium, and at Castillo, in northern Spain. These rare exceptions to the open camps would tend to prove that the caverns were sought rather for protection from enemies and as rain shelters than as retreats from a bitter-cold climate. In the valley of the Beune, a small tributary of the Vézère, in Dordogne, we find a true Acheulean station quite close to the river shore. This proves that in Acheulean times this valley was already deepened to the same degree as it is to-day. In the valley of the Somme the Acheulean culture stretches from the 'highest terrace' down below the present level of the river, which has made for itself a new high channel. The fact that two Acheulean stations are found on the upper Garonne, high above the present water-level, is of little significance, as at that time the water-level was also high. In general the Acheulean flint workers preferred the open stations throughout all Acheulean times, and their camps are found on the open plateaus between the rivers or on the various 'terrace' levels, as on the higher, middle, and lower 'terraces' of the Somme at St. Acheul, or again close along the borders of the rivers and streams, as in the Dordogne region. Even during the early Acheulean stage a dry climate had begun to prevail in certain parts of Germany. Near Metz is the 'older loess' station of Sablon, which was occupied in early Acheulean times, indicating a warm period of arid climate favorable to the transportation of the wind-blown 'loess'; doubtless, this fine dust at times filled the entire atmosphere and obscured the sun, as is the case to-day on the high steppes and deserts of eastern Asia. An exception to the open-country life preferred by the Acheulean flint workers is found in the great grotto[AD] of Castillo, near Puente Viesgo, in the Province of Santander, northern Spain. The deposits which filled this grotto to a thickness of 45 feet from the floor to the roof were explored by Obermaier, who found them divided into thirteen layers, covering eleven periods of industry and presenting the most wonderful epitome of the prehistory of western Europe from Acheulean times to the Age of Bronze, in Spain (Fig. 79). [Illustration: FIG. 78. Entrance (white cross) to the great grotto of Castillo in northern Spain. This grotto was frequented by the Men of the Old Stone Age from Acheulean to Azilian times, an archæologic sequence surpassed only by that of the open camps along the terraces of the Somme. Photograph from Obermaier.]