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Rh November, 1607. Fifteen thousand Indians were employed upon this work, and as a number of airshafts (lumbreras) were sunk, in order to enable them to work upon several different points at once, in eleven months a tunnel (Socabon) of 6,600 metres in length, three metres five in breadth, and four metres two in height, was concluded.

From the Northern extremity of this Socabon, (La boca de San Gregorio,) an open cut of 8,600 metres conducted the waters to the Salto (fall) of the river Tula, where, quitting the valley of Mexico, they precipitate themselves into that of Tula, from a natural terrace of twenty Mexican varas in height, and take their course towards the Bar of Tampico, where they enter the Mexican Gulph. An enterprize of such magnitude, concluded with such extraordinary expedition, could hardly be free from defects; and Martinez soon discovered that the unbaked mud bricks, (Tĕpĕtātĕ,) of which the interior of the Socabon was composed, were unable to resist the action of the water, which, being confined within narrow limits, was at times impelled through the tunnel with irresistible violence. A facing of wood proved equally ineffectual, and masonry was at last resorted to; but even this, although successful for a time, did not answer permanently the purpose for which it was intended, because the engineer, instead of an elliptical arch, constructed nothing but a sort