From the extreme NORTH WEST--the British possessions near Lake Winnipeg--accounts of very disastrous floods have been received. The settlement established by the Earl of Selkirk in 1812, which had grown into considerable importance as a point from which supplies were furnished to the Fur Companies of that region, and which contained about ten thousand inhabitants, had been nearly destroyed by freshets in the Red River of the North, which began on the 5th of May, and reached their height about the 20th. Dwellings, crops, and nearly all the products of twenty-five years' labor have been swept away: the damage is estimated at about a million of dollars. SOUTH AMERICA. From the _Argentine Republic_ we have intelligence of fresh political disturbances, indicating at least the temporary failure of the new and moderate system introduced by Urquiza after the defeat and expulsion of Rosas. The Convention from the several provinces summoned by Urquiza, met at San Nicholas--ten of the thirteen provinces being represented by their governors, and adopted a Constitution for the federation. It provided for abolishing the transit duties, and for the assembling of a Congress at Santa Fé, which was to consist of two delegates from each province, to be selected by the popular vote, to be untrammeled by instructions, and the minority to conform to the decision of the majority, without dissent or protest. In order to defray the national expenses, the provinces agreed to contribute in proportion to the product of their foreign Custom-houses, and that the permanent establishment of the duties shall be fixed by Congress. To secure the internal order and peace of the republic, the provinces engage to combine their efforts in preventing open hostilities or putting down armed insurrections, and the better to promote these objects, General Urquiza was recognized as General-in-chief of the armies of the Confederation, with the title of Provisional Director of the Argentine Confederation. In the Chambers of Buenos Ayres, very warm opposition was manifested to this Convention: bitter and violent debates took place, and the popular clamor became so high that the Governor Lopez resigned his office; whereupon General Urquiza dissolved the Chambers, and took the supreme power into his own hands. In a communication sent by his order to the British Chargé, he states that the anarchy into which the province was thrown, compelled him to take this step, and declares that he shall not extend the authority with which he is vested beyond the time and the measures necessary for the re-establishment of order in the province. He also issued a brief address to the Governors of the provinces of the Confederation, declaring that he should use the power they had conferred upon him in rendering effective the sovereign will of the nation, in repelling foreign aggressions, and in restraining the machinations of those who might seek to awaken the