The Confederates were now cut off both above and below; for the position of Island Number Ten was at the lower point of a V-shaped bend in the Mississippi, with Federal forces at the two upper points. But the Federal troops could not close on the Confederates without crossing over to the east bank; and their transports could not run the gauntlet like the ironclads. So the Engineer Regiment of the West cut out a water road connecting the two upper points of the V. This admirable feat of emergency field engineering was effected by sawing through three miles of heavy timber to the nearest bayou, whence a channel was cleared down to New Madrid. Then the transports went through in perfect safety and took Pope's advanced guard aboard. The ironclad _Pittsburg_ had come down, through another thunderstorm, this same morning of the seventh; and when the island garrison saw their position completely cut off they surrendered to Foote. Next day Pope's men cut off the greater part of the Confederates on the mainland. Thus fell the last point near Johnston's original line along the southern borders of Missouri and Kentucky. Just before it fell Johnston made a desperate counterattack from his new line at Corinth, in northwest Mississippi, against Grant's encroaching force at Shiloh, fifteen miles northeast, on the Tennessee River. Writing "A. S. Johnston, 3d April, 62, _en avant_" on his pocket map of Tennessee, the Confederate leader, anguished by the bitter criticism with which his unavoidable retreat had been assailed, cast the die for an immediate attack on Grant before slow Halleck reinforced or ready Buell joined him. Johnston's lieutenants, Beauregard and Bragg, had obtained ten days for reorganization; and their commands were as ready as raw forces could be made in an extreme emergency. They hoped to be joined by Van Dorn, whose beaten army was working east from Pea Ridge. But on the second they heard that Buell was approaching Grant from Nashville; and on the third Johnston's advanced guard began to move off. Van Dorn arrived too late. The march, which it was hoped to complete on the fourth, was not completed till the fifth. The roads were ankle-deep in clinging mud, the country densely wooded and full of bogs and marshes. The forty thousand men were not yet seasoned; and, though full of enthusiasm, they neither knew nor had time to learn march discipline. Moreover, Johnston allowed his own proper plan of attacking in columns of corps to be changed by Beauregard into a three-line attack, each line being formed by one complete corps. This meant certain and perhaps disastrous confusion. For in an attack by columns of corps the firing line would always be reinforced by successive lines of the same corps; while attacking by lines of corps meant that the leading corps would first be mixed up with the second, and then both with the third.