Pittsburgh has produced many eminent men in law, politics and divinity, and is now the residence of the erudite, acute and witty author of the Memoir of Sebastian Cabot, which should be read by every native American. Its manufacturing powers and propensities have been so often described and lauded that we shall say nothing about them, except that they fill the people's pockets with cash, and their toiling town with noise, and dust, and smoke.

Pittsburgh is full of good things in the eating and drinking way, but it requires much ingenuity to get them down your throat unsophisticated with smoke and coal-dust. If a sheet of white paper lie upon your desk for half an hour, you may write on it with your finger's end, through the thin stratum of coal-dust that has settled upon it during that interval.

The Pittsburghers have committed an error in not rescuing from the service of Mammon, a triangle of thirty or forty acres at the junction of the Alleghany and Monongahela, and devoting it to the purposes of recreation. It is an unparalleled position for a park in which to ride or walk or sit. Bounded on the right by the clear and rapid Alleghany rushing from New York, and on the left by the deep and slow Monongahela flowing majestically from Virginia, having in front the beginning of the great Ohio, bearing on its broad bosom the traffic of an empire, it is a spot worthy of being rescued from the ceaseless din of the steam engine, and the lurid flames and dingy smoke of the coal furnace. But alas! the sacra fames auri is rapidly covering this area with private edifices; and in a few short years it is probable, that the antiquary will be unable to discover a vestige of those celebrated military works, with which French and British ambition, in by-gone ages, had crowned this important and interesting point.

There is a large bridge of timber across the Alleghany and another over the Monongahela; the former of which leads to the town of Alleghany, a rapidly increasing village, situated on a beautiful plain on the western side of the river. About half a mile above the bridge the Alleghany is crossed by an aqueduct bringing over the canal, which (strange to say) comes down from the confluence of the Kiskeminetas with the Alleghany on the western side of the latter river. The aqueduct is an enormous wooden trough with a roof, hanging from seven arches of timber, supported by six stone piers and two abutments. The canal then passes through the town and under Grant's hill through a tunnel, and communicates by a lock with the Monongahela.

The field of battle on which the conceited Braddock paid with his life the penalty of obstinate rashness, is not far from Pittsburgh, and is interesting to Americans as the scene on which the youthful Washington displayed the germs of those exalted qualities which afterwards ripened into the hero, and made him the founder and father of a nation.

Pittsburgh is destined to be the centre of an immense commerce, both in its own products and those of distant countries. Its annual exports at present probably exceed 25,000 and its imports 20,000 tons. Its trade in timber amounts to more than six millions of feet. The inexhaustible supply of coal and the facility of obtaining iron, insure the permanent success of its manufactories. Pittsburgh makes steam engines and other machinery, and her extensive glassworks have long been in profitable operation. There are also extensive paper mills moved by steam, and a manufactory of crackers (not explosive but edible) wrought by the same power. These crackers are made of good flour and pure water, and are fair and enticing to the eye of hunger, but we do not find the flavor so agreeable to the palate as that of Wattson's water crackers. Perhaps they are kneaded by the iron hands of a steam engine, whereas hands of flesh are needed to make good crackers.

New Yorkers and people from down east, who wish to visit the Virginia Springs, cannot take an easier and more delightful route, than that through Pennsylvania to Pittsburg, and thence down the Ohio to Guyandotte; whence to the White Sulphur the distance is one hundred and sixty miles over a good road, through a romantic country, and by a line of good stage coaches.

Letter X is dated “Johnstown, August 20.” Mr. P. left Pittsburgh on the 18th, at nine in the evening, in the canal packet Cincinnati, Captain Fitzgerald. In a few minutes after moving, the packet entered the aqueduct which carries the canal over to the western bank of the Alleghany, “along which it runs in a north eastern direction for thirty miles.” At five o'clock on the morning of the 19th, our tourist passed the village of Freeport, which stands on the western bank of the Alleghany, below the mouth of the Kiskeminitas. A few minutes afterwards he crossed the Alleghany through an aqueduct, which “carries the canal over that river to the northern bank of the Kiskeminitas, the course of which the canal now pursues in a south eastern direction.”

At eight A. M. Mr. P. passed Leechburg, at twelve Saltsburgh—and at two P. M. an aqueduct leading the canal into a tunnel eight hundred feet long, going through the mountain and cutting off a circuit of four miles. At 3 A. M. on the 20th, Johnstown is reached, “the eastern end of the trans-Alleghanian canal, and the western beginning of the Portage rail road.”

Letter XI gives a vivid picture of the Portage rail road. This also we will be pardoned for copying.