THE START FOR THE GULF.-- CAUGHT IN THE ICE-RAFT.-- CAMPING ON THE OHIO.-- THE GRAVE CREEK MOUND.-- AN INDIAN SEPULCHRE.-- BLENNERHASSET'S ISLAND.-- AARON BURR'S CONSPIRACY.-- A RUINED FAMILY. UPON arriving at Pittsburgh, on the morning of December 2d, 1875, after a dreary night's ride by rail from the Atlantic coast, I found my boat--it having preceded me--safely perched upon a pile of barrels in the freight-house of the railroad company, which was conveniently situated within a few rods of the muddy waters of the Monongahela. The sneak-box, with the necessary stores for the cruise, was transported to the river's side, and as it was already a little past noon, and only a few hours of daylight left me, prudence demanded an instant departure in search of a more retired camping-ground than that afforded by the great city and its neighboring towns, with the united population of one hundred and eighty thousand souls. There was not one friend to give me a cheering word, the happy remembrance of which might encourage me all through my lonely voyage to the Gulf of Mexico. The little street Arabs fought among themselves for the empty provision-boxes left upon the bank as I pushed my well-freighted boat out upon the whirling current that caught it in its strong embrace, and, like a true friend, never deserted or lured it into danger while I trusted to its vigorous help for more than two thousand miles, until the land of the orange and sugar-cane was reached, and its fresh, sweet waters were exchanged for the restless and treacherous waves of the briny sea. Ah, great river, you were indeed, of all material things, my truest friend for many a day! The rains in the south had filled the gulches of the Virginia mountains, the sources of the Monongahela, and it now exhibited a great degree of turbulence. I was not then aware of the tumultuous state of the sister tributary, the Alleghany, on the other side of the city. I supposed that its upper affluents, congealed during the late cold weather, were quietly enjoying a winter's nap under the heavy coat in which Jack Frost had robed them. I expected to have an easy and uninterrupted passage down the river in advance of floating ice; and, so congratulating myself, I drew near to the confluence of the Monongahela and Alleghany, from the union of which the great Ohio has its birth, and rolls steadily across the country a thousand miles to the mightier Mississippi. The current of the Monongahela, as it flowed from the south, covered with mists rising into the wintry air,--for the temperature was but a few degrees above zero,--had not a particle of ice upon its turbid bosom.