viceroy, accompanied by the audiencia and canons; papers drawn up by the fiscal and other lawyers; advices given by the monks of St. Francis; an active impetuosity every fifteen or twenty years, when the lakes threatened an overflow; and a tardiness and culpable indifference whenever the danger was past. Twenty-five millions of livres * were expended, because they never had courage to follow the same plan, and because they kept hesitating for two centuries between the Indian system of dikes and that of canals, between the subterraneous gallery (80cabon), and the open cut through the mountain (tajo abierto). The gallery of Martinez was suf fered to be choaked up, because a large and deeper one was wished; and the cut (tajo) of Nochistongo was neglected to be finished, while they were disputing about the project of a canal of Tezcuco, which was never executed. The desague in its actual state is undoubtedly one of the most gigantic hydraulical operations ever executed by man. We look upon it with a species of admiration, particularly when we consider the nature of the ground, and the enor mous breadth, depth, and length of the aper ture. If this cut were filled with water to the depth of 10 metres †, the largest vessels of war * 1,041,750l. sterling. Trans. 32.8 feet. Trans. could pass through the range of mountains which bound the plain of Mexico to the north east. The admiration which this work inspires is mingled, however, with the most afflicting ideas. We call to mind at the sight of the cut of Nochistongo the number of Indians who perished there, either from the ignorance of the engineers, or the excess of the fatigues to which they were exposed in ages of barbarity and cruelty. We examine if such slow and costly means were necessary to carry off from a valley inclosed in on all sides so inconsiderable a mass of water; and we regret that so much collective strength was not employed in some greater and more useful object; in opening, for example, not a canal, but a passage through some isthmus which impedes navigation. The project of Henry Martinez was wisely conceived, and executed with astonishing rapidity. The nature of the ground and the form of the valley necessarily prescribed such a subterraneous opening. The problem would have been resolved in a complete and durable manner; 1. if the gallery had been commenced in a lower point, that is to say, corresponding to the level of the inferior lake; and, 2. if this gallery had been pierced in an elliptical form, and wholly protected by a solid wall equally elliptically vaulted. The subterraneous passage executed by Martinez contained only 15 square metres in section, as we have already observed. To judge of the dimensions necessary for a gallery of this nature, we must know exactly the mass of water carried along by the river of Guautitlan and the lake of Zumpango at their greatest rise. I have found no estimation in the memoirs drawn up by Zepeda, Cabrera, Velasquez, and by M. Castera. But from the researches which I have myself made on the spot, in the part of the cut of the mountain (el corte o tajo) called la obra del consulado, it appeared to me that at the period of the ordinary rains the waters afford a section of from eight to ten square metres †, and that this quantity increases in the extraordinary swellings of the river Guautitlan to 30 or 40 square metres §. The Indians assured me, that in this last case, the water-course which forms the bottom of the tajo is filled to such a § The engineer Iniesta advanced even, that in the great rises the water ascends to the height of 20 or 25 metres (65 or 82 feet) in the canal near the Boveda Real. But Velasquez affirms that these estimations are enormously exaggerated. (Declaracion del Maestro Iniesta, and Informe de Velasquez, both in manuscript). degree, that the ruins of the old vault of Martinez are completely concealed under water. Had the engineers found great difficulties in the execution of an elliptical gallery of more than from four to five metres* in breadth, it would have been better to have supported the vault by a pillar in the centre, or to have opened two galleries at once, than to have made an open trench. These trenches are only advantageous when the hills are of small elevation and small breadth, and when they contain strata less subject to falling down. To pass a volume of water of a section in general of eight †, and sometimes from 15 to 20 square metres, it has been judged expedient to open a trench, of which the section for a considerable distance is from 1800 to 3000 square metres §. In its present state the canal of derivation (desague) of Huehuetoca contains, according to the measurements of M. Velasquez, * From 13 to 16 feet. Trans. +86 square feet. Trans. From 161 to 215 square feet. Trans. § From 19,365 to 32,275 square feet. Trans. Informe y exposicion de las operaciones hechas para examinar la possibilidad del desague general de la Laguna de Mexico y otros fines a el conducientes, 1774 (manuscript me moir, folio 5.). From the sluice of Vertideros Mex, varas. to the bridge of Huehuetoca, From the bridge of Huehuetoca to the sluice of Santa Maria From the Compuerta de Santa Maria to the sluice of Valderas From the Compuerta de Valderas to la Boveda Real Metres. 4870 or 4087 2660 2232 1400 1175 3290 2761 In this length of 43 common leagues, the chain of the hills of Nochistongo (to the east of the *67,535 feet. Trans. |