The slave-trade has been extensively pursued in the Congo. A British steam-cruiser, for many years, has been stationed off its mouth, making many captures. Under American nationality, however, several vessels have entered, taken in a cargo of slaves and escaped. The natives, near the mouth of the river, have been rendered treacherous and cruel by the slave-trade; but a short distance in the interior, they are represented as being civil and inoffensive, disposed to trade in elephants’-teeth and palm-oil. After crossing the Congo, the Perry communicated with Kabenda, and the day following anchored at Loango, in company with the British cruiser stationed off that point. The British commodore arriving the next day, a letter was addressed to him, dated April 4th, asking whether any suspected vessels had been seen on the south coast, by the cruisers under his command, since the capture of the Chatsworth, on the 11th of September, 1850; also requesting that he would express his views of the present state of the slave-trade on the southern coast of Africa. In reply, the British commodore made the following communication: “I beg to acquaint you that the only report I have received of a suspected vessel, under American colors, having been seen on the south coast since the date you have named, was from H. M. steam-sloop Rattler, of a schooner showing American colors having approached the coast near Old Benguela Head; which vessel, when Commander Cumming landed subsequently, was reported to him, by the people on shore, to have shipped slaves near that place. “Your inquiry applies only to the south coast; but it will not be irrelevant to the general subject and object for which we are co-operating, if I add that the schooner Bridgeton, of Philadelphia, under the American flag, was visited by Her Majesty’s steam-sloop Prometheus, off Lagos, on the 22d of August, under circumstances causing much suspicion, but with papers which did not warrant her seizure by a British officer; and that I have since received information from Her Britannic Majesty’s consul at Bahia, that the same vessel landed three hundred slaves there in October. “I also take this opportunity of bringing under your notice another American vessel, which I observed at Sierra Leone under the American flag; and which was reported to me, by the authorities there, as being to all appearance a legal trader, with correct papers, but whose real character and ultimate object I have since had much reason to doubt.