of Sixty dollars per Lot as aforesaid to be paid to the proprietors, and all that said Lots may be sold for over said average value of sixty dollars per Lot, when platted is to be equally divided & distributed between said proprietors and said Smith— And said proprietors on their part agree and bind themselves to pay off & satisfy the incumbrances that exist against said property in favor of the school fund of said Township so fast as the sales of the property mortgaged will enable them to do so— Said parties hereto in consideration of the premises hereby further agree and bind themselves semi annually to add to the estimated average value of sixty dollars per Lot twelve per cent per hundred on the lots remaining unsold at said semi anual re◊ts which occur on the 22nd day of August and February in each and every year;— said interest at twelve per cent to abate whenever said mortgaged premises shall by the sales thereof as aforesaid shall yielded a sum sufficient to satisfy the incumbrances on the same—