(b) an inclined plane from each inclined plane described in paragraph (a), at right angles thereto and rising therefrom at a ratio of 1 foot measured vertically to 40 feet measured horizontally to an imaginary horizontal line drawn at right angles through the centre line of each strip, as produced, at a point 17,500 feet from each strip end measured horizontally and 387.5 feet above the elevation at each strip end measured vertically, the outer limits of which imaginary inclined plane is 2,000 feet throughout from the produced centre line of the strip.