At the same time the general began to concentrate his forces at the mouth of Portage river. The greatest activity was visible in camp; in preparing for the descent on Canada--boats were collected--beef jerked--the superfluous baggage secured in block houses and a substantial log fence two miles long, extending from Portage river to Sandusky bay, was built to secure the horses during the operations of the army. On the 17th Gov. Shelby with four thousand volunteers arrived at head quarters. This formidable corps were all mounted; but it was deemed best for them to act as infantry, and leave their horses on the peninsula. On the 20th Gen. M'Arthur's brigade from Fort Meigs joined the army after a very fatiguing march of three days down the lake coast. Col. Johnson's mounted regiment remained at Fort Meigs, but had orders to approach Detroit by land and to advance _pari passu_ with the commander in chief, who was to move in boats thro' the islands to Malden, and of whose progress the colonel was to be daily informed by a special express. The British prisoners taken in the naval action of the 10th, were sent to Chilicothe, guarded by a detachment from Col. Hill's regiment of Pennsylvania detached militia. The different posts on the American side of the lake were left in charge of the Ohio Militia. Fort Meigs, which till now had covered eight acres of land, was reduced in its dimensions to one acre. About five hundred Kentuckians were to remain at Portage to guard the stores and horses, being upwards of five thousand in number, which were left on the Peninsula during the absence of the army. Every thing being now ready, the embarkation of the troops commenced at the dawn of day, on the 21st. For the want of a sufficient number of boats, not more than one third of the number could embark at once. There is a range of islands extending from the head of the Peninsula to Malden. These islands render the navigation safe, and afford the army convenient depot for baggage and stores, as well as halting places. Put-in-bay island, sixteen miles from Portage, was selected by the General as the first point of rendezvous--the first stage in his passage across the lake. The weather was favorable. As soon as the first division of boats reached the island, men were immediately detached to take back the boats for a fresh load. Such was the eagerness of the men to accelerate the embarkation of the whole army, that they, in most cases, anticipated this regulation by volunteering their services to return with the boats. Every one courted fatigue. The fleet under Com. Perry, was busily engaged in transporting the baggage of the army. In the course of the 22d the whole army gained the island, and encamped on the margin of the bay, which forms nearly a semi-circle.