Some of the erratic blocks were as large as houses, but, being used as quarries, they are fast disappearing. One of them at Pianezza, at the mouth of the Susa valley, is 80 feet long, 40 feet broad, and 46 feet high, and a chapel has been built upon it. The huge erratic blocks in the hills between the two arms of the Lake of Como have supplied materials for the monolithic columns of the churches and palaces in the environs. The slopes of the hills of Turin facing the Alps are likewise covered with erratic blocks. * * * * * When the glaciers retired into the upper valleys of the Alps, the soil which they covered was left bare, and the depressions now occupied by the beautiful lakes of Lombardy were revealed. These depressions, whose bottom even now sinks down below the level of the ocean, were formerly arms of the sea, in character very much like the fiords of Norway. That such was the case is proved by the presence, in every one of the Lombard lakes, of a sardine (the _agone_), which naturalists consider to be a sea fish. In Garda Lake, moreover, there still dwell two marine fishes which have adapted themselves to their new condition of life, as well as a small marine shell-fish. [Illustration: Fig. 58.—ANCIENT LAKES OF VERBANO.] The number of these Alpine lakes was much larger formerly, and those which still exist shrink from year to year. In Upper Piemont alluvial deposits have long ago filled up the lakes, and there now only remain a few pools of {198} water to indicate their site. The first sheets of water to which the term “lake” may fairly be applied are met with on both banks of the Dora Baltea (see Fig. 57). The little basin of Candia and the shallow Lake of Azeglio, to the west and east of the river, are the only remains of _Lacus Clisius_, which covered an area of several hundred square miles until its waters broke through the semicircular terminal moraine which bounded it on the south. The Dora Baltea formerly escaped from this lake in the south-east, its present course only dating from the fourteenth century. [Illustration: Fig. 59.—THE UPPER EXTREMITY OF THE LAKE OF COMO. Scale 1 : 148,000.] Since this reservoir has been drained, the first lake of importance in the west is that of Verbano, very inappropriately called Lago Maggiore, or the “principal lake,” as that of Garda exceeds it in extent. Ancient beaches, at an elevation of 1,300 feet above the sea, prove that the waters of the lake have considerably subsided, and that its area was much larger formerly; and it curiously ramified with neighbouring lake basins, now merely connected with it by rivers. The ancient moraine at the foot of this lake, and through which the Ticino has excavated itself a passage, still rises to a height of 980 feet. {199}