Section 7. Land taken for or held as a park under this chapter shall be forever kept open and maintained as a public park, and no building which exceeds six hundred square feet in area on the ground shall be erected on a common or park dedicated to the use of the public without leave of the general court; but, except in parks in Boston and in parks comprising less than one hundred acres in extent, structures for shelter, refreshment and other purposes may be erected of such material and in such places as, in the opinion of the fire commissioners, if any, do not endanger buildings beyond the limits of such park. The superior court shall have jurisdiction in equity, upon petition of not less than ten taxable inhabitants of the city or town in which such common or park is located, to restrain the erection of a building on a common or park in violation of this section.