mentioned. Every such debt shall be authorized by law for some purpose or purposes, to be distinctly specified therein; and every such law shall provide for levying an annual tax sufficient to pay the interest semiannually, and the principal within twenty years from the passage of such law, and shall specially appropriate the proceeds of said taxes to the payment of said principal and interest; and such appropriation shall not be repealed nor the taxes postponed or diminished until the principal and interest of said debts shall have been wholly paid. Every contract of indebtedness entered into or assumed by or on behalf of the State, when all its debts and liabilities amount to said sum before mentioned, shall be void and of no effect, except in cases of money borrowed to repel invasion, suppress insurrection, defend the State in time of war, or, if hostilities be threatened, provide for the public defense. The State, notwithstanding the foregoing limitations, may, pursuant to authority of the Legislature, make and enter into any and all contracts necessary, expedient or advisable for the protection and preservation of any of its property or natural resources, or for the purposes of obtaining the benefits thereof, however arising and whether arising by or through any undertaking or project of the United States or by or through any treaty or compact between the states, or otherwise. The Legislature may from time to time make such appropriations as may be necessary to carry out the obligations of the