I may as well state here the explanation, as we afterwards learned it, of this most unexpected reappearance of the enemy,--which came upon General Walker like a thunderclap, whilst he dreamed they had left him for good and all. It seems that the Vanderbilt Company, whom Walker had made enemies by ousting them from the Transit route, sent an agent (one Spencer) to the disheartened Costa Ricans, who showed them that they might easily strangle the filibuster force by seizing the ill-guarded Rio San Juan. Led by Spencer, they secretly cut a road through the forest on the Costa Rican side, found the forts scarcely watched by a few spiritless sick men, and overwhelmed and scattered them without difficulty. At the same time they surprised and seized all the Transit steamers on the river and lake, so that thenceforward communication with the Atlantic was closed to General Walker, and a large body of New Orleans recruits under Lockridge, who had just arrived at the mouth of the river, found themselves headed off, and began a long and skilless fight to recover the steamers and make the junction with the isthmus force. So, after all, Walker owes his defeat, not to the natives of Central America, but to his own countrymen; and, had it not been for the malice or revenge of Vanderbilt, he might have reigned in Nicaragua at this day,--unless he had blundered himself out of it unassisted, as many who lived with him thought he could hardly fail to do, were time but granted him.--After capture of the lake steamers, the Costa Ricans, impressing their American crews into service, took them up to Granada to embark the old force of Costa Ricans and Chamorristas still remaining there. They were on this errand when the steamer San Carlos was first seen to pass Virgin Bay. But what other reinforcement they expected, whilst they lay so long against the island after their return from Granada, I do not know,--unless it was the Guatemalans, who we knew soon afterward had joined them in large force.