A large portion of the area bounded by the crystalline rocks of Olympus and Ossa, and by the cretaceous range of the Pindus, running parallel with the former, consists of plains originally covered by vast lakes. The Gulf of Volo approaches close to the shrunken remains of one of these lakes—that of Karla, or Bœbeis—into which the waters of the swampy plain of Larissa discharge themselves. The dwellers on the shores of this lake say that a dull rumbling noise may now and then be heard at its bottom, which they ascribe to the bellowing of some invisible animal, but which is more probably the gurgling sound of the water penetrating into a sink-hole. Other lake basins are met with at the foot of Olympus towards the west and north-west, and some of the valleys of the upper tributaries of the Peneus are covered with alluvium left behind by the receding waters. Hercules, according to some—Neptune, according to others—drained all these lakes of Thessaly into the Ægean, by opening the narrow gorge between Olympus and Ossa, known to the ancients as the Valley of Tempe. This narrow valley is due, no doubt, to the slow erosive action of water. To the Hellenes it realised their ideals of refreshing coolness and beauty, and once every nine years an embassy arrived from Delphi to pluck the laurel-leaves destined for the victors in the Pythian games. The {113} Valley of Tempe is indeed most beautiful; the transparent and rapid waters of the Peneus, the foliage of the planes, the shrubberies of laurel-roses, and the red-hued cliffs—these combine frequently, and form pictures which delight the senses and impress the mind. But, taken as a whole, this narrow and sombre valley fairly deserves its modern name of Lykostomo, or “wolf’s gorge.” Even in Thessaly, and, above all, in the Pindus, there are localities more smiling and more beautiful than this famous Valley of Tempe. The upper valleys of the Peneus, or Salembria, abound in natural curiosities, such as defiles, sinks, and caverns. To the north-west of Mount Olympus, the turbid Titaresius flows through the narrow gorge of Saranta Poros, or of the Four Fords, which was looked upon in former times as one of the gates of hell.