So far as I know, riflemen had never before been posted in trees to check the advance of an army through a broken and forest-clad country; but the scheme was a good one, and it was carried out with thoughtful attention to every detail. The sharp-shooters were generally hidden in carefully prepared nests of leaves; some of them had tunics of fresh palm-leaves tied around their bodies from the shoulders down, so that at a little distance they could not be distinguished from the foliage of the trees in which they were concealed; and in a few cases that were reported to me they wore under their leafy tunics double canvas jackets filled with sand and carefully quilted, as a partial protection from bullets. This swarm of tree-men formed the Spanish skirmish-line, and a most dangerous and effective line it was, for the reason that it could be neither seen, driven in, nor dislodged. The hidden marksmen used Mauser rifles with smokeless powder, and although our men heard the reports and were killed or disabled by the projectiles, they had no guide or clue whatever to the location of their assailants. A skirmish-line in thickets or clumps of chaparral on the ground might have been driven back as our army advanced, and thus our rear would have been all the time secure from attack; but a skirmish-line hidden in tree-tops was as dangerous to the rear as to the front, and a soldier pressing forward toward what he supposed to be the enemy's position was just as likely to get a Mauser bullet in his back as in his breast. Scores of wounded men who were brought into the First Division field-hospital on Friday and Saturday had never seen a Spanish intrenchment, or had even so much as a glimpse of a Spanish soldier. In spite of the deadly fire to which they were subjected from front, sides, and rear, our troops pushed on, as rapidly as the congested state of the trail would permit, toward the ford of the San Juan River. The loss which our advance sustained at this point was greatly increased by the sending up of an observation balloon, which hung over the road, just above the trees, and not only attracted the fire of the Spaniards in front, but served their artillerymen as a target and a range-finder. It was an even better firing guide than the sheets of iron or zinc roofing which they had put up in some of the openings through which the trail ran; and until it was finally torn by shrapnel so that it slowly sank into the forest, the men under and behind it were exactly in the focus of the converging streams of bullets which it attracted from all parts of the San Juan heights. The only useful discovery made by it was the fact that there was a second or branch trail leading to a lower ford of the San Juan River which General Kent's division might take, and thus relieve the crowding on the main road.