Let us resume our description of the Isthmus, in order that we may be in a position to understand the conditions with which the engineers have to deal. The practicability of the Panama route is due to the fact that rivers have already done a great part of the excavation, and if desert conditions had supervened--if there were, as at Suez, practically no rainfall--the construction of a tide-level canal would be simply the excavation of a trench in dry material, which would be filled by the inflowing waters of the sea. A tidal lock being added to regulate the ebb and flow at Panama (for the Atlantic side is tideless), the canal would be complete. But as things actually are, the rainfall on the Isthmus is very heavy, particularly on the Atlantic side, where it reaches 140 inches[5] per annum, and the rivers have at all times considerable bodies of water, and during the rainy season (commencing in May) are subject to sudden and violent freshets. The Chagres at Gamboa has been known to rise 35-1/2 feet in 24 hours.[6] Suppose then that a tide-level trench were suddenly formed across the Isthmus, as by a convulsion of nature. We should then see the rivers pouring into this fjord in a number of cascades of various height. Of these the greatest would be the Chagres cascade, entering from the east near Gamboa and Obispo. The height of the waterfall would be 46 feet in the driest season and as much as 80 feet in occasional floods.[7] [5] Abbot, "Problems of the Panama Canal," p. 96. [6] _Loc. cit._, p. 146. [7] Abbot, _loc. cit._, p. 116. [Illustration: EXCAVATION NEAR TAVERNILLA.] [Illustration: RIVER CHAGRES AND RAILWAY NEAR GORGONA.]