National Geographic : 1916 Jul
IN THE VALLEY OF MEXICO The Valley of Mexico is a semi-arid plateau, a mile and a half higher than Washington, D. C., andissurrounded inturn by high mountains, with only a few natural passages. Its greatest length is 71 miles and its greatest width 45 miles, although its average length isless than 50miles and its average width less than 40. When the mountains which surround the valley were thrown up byvolcanic cataclysms, they are supposed to have inclosed the valley entirely. During ages that followed the valley was a large lake, with numerous islands dotting its surface. Inthe day of the Aztecs the water had subsided, leaving many small lakes instead of the one large one. The coming ofthe Spaniard resulted inthe cutting of a drainage canal through the mountain and the disappearance of most of these lakes.