"In consideration only of the completion of the work hadled under separate contract, in which the party of 2nd parts indentures to remove 200 cu yds soil bordering on ice pond and to spread same and house, this additional contract be here entered into. P.S. 2d parties to remove sufficient additional soil (to produce a lake at the site of the old ice pond whose sides shall conform with the natural slope of the former ice pond and its dirt embankment, if a water depth of one foot below the level of the present spillway. And join to present spillway the said side also be packed with even slopes to conform to that of the said slopes of ice pond. But adjacent the boundary line of the adjy property, now the property of C.P.B. Decker the sides shall be vertical. And Subject to the completion of the other described works in a manner satisfactory to the part of 1st party; the said P.S. shall p.g to 2d parties, the sum hereby set but this may not become due until after the p.f.p. shall be approved the work.