It is computeu by the Monlrcal Courier, that therc are about 20,000 Negroes in Canada wlio have escapee! from slavery in the Southern States. An attempt is making to induce the colored population to emegrate to Jamaca. The results of the abolition of Slavery in ihjjj West Ir.dies have boen that thsusands of t;;: brrner slavcs havo becotne treeholderi , and such is the scarcily of labor, and the high premium it commands ia the West India market, that the Legislatura of the lsland of Jamaca passed last year, an net offering a free passage under the most favorable circumslanccp, to all persons wtlling to emigrate to that Colony. J. W, Dunscomb, has boen appointed agent for Canada, with aulhoriiy toassistsuch ns are willing to emicrate.