The General Assembly may provide, by Law, for organizing new Counties, locating and removing county seats, and changing county lines; but no new county shall be organized without the consent of the majority of the legal voters residing within the limits proposed to be formed into said new county; and whenever a new county shall be proposed to be formed out of portions of two or more counties, the consent of a majority of the legal voters of such part of each of said counties, respectively, shall be required; nor shall the lines of any county nor of Baltimore City be changed without the consent of a majority of the legal voters residing within the district, which under said proposed change, would form a part of a county or of Baltimore City different from that to which it belonged prior to said change; and no new county shall contain less than four hundred square miles, nor less than ten thousand inhabitants; nor shall any change be made in the limits of any county, whereby the population of said county would be reduced to less than ten thousand inhabitants, or its territory reduced to less than four hundred square miles. No county lines heretofore validly established shall be changed except in accordance with this section.