THE FREE NEGROES OF MARYLAND. – The fact brought to notice by the recent Slaveholder’s Convention, that the free blacks constitute more than one-eighth of the entire population in Maryland, excites no little surprise. Few at the North were prepared to hear that they were so numerous, though an examination of that much-neglected volume, the census returns of 1850, would have revealed the state of the case. The Albany Evening Journal, sharing the general misapprehension, speaks of the free negroes of Maryland as “a few hundred.” Mr. PEARCE, on the hand, states their present number at 80,000. In the State of New York, by the census of 1850, we had 49,069 colored people. If they were proportionally as numerous here as in Maryland, we should have to-day 400,000, or ten times the actual number. A Baltimore journal says that more than half the free blacks of the State reside in that City, where the returns of the Savings Banks, as well as the condition of the churches and societies supported by them, evince their perfect ability to take care of themselves when they have an opportunity for employment and improve it. Slavery in Maryland exists mainly in the country, on large farms. The towns, including the large commercial City of Baltimore, are favorable to freedom.