Also all the property, land and buildings situated on the south-westerly side of the following line, to wit: beginning at a point on the northerly side of the above-mentioned passage-way for vessels twenty-two feet nine inches east of the easterly line of the roadway draw over said passage-way, and running northerly at right angles to said passage-way, one hundred and three feet five inches, to a point where said line intersects with the north-easterly line of said Fitchburg Railroad bridge over Charles River; thence northerly, following and coinciding with said north-easterly line of bridge, eight hundred and forty-eight feet; thence turning and running westerly to a point in the north rail of the north passenger track of the Fitchburg Railroad, distant four hundred and sixteen feet seven inches from the south-easterly line of Austin Street, measured on said north rail of the north track. Said point is also distant twenty-nine feet four inches at right angles from the southerly side of the wooden freight house (measured from a point sixty feet distant from the westerly end) belonging to the Fitchburg Railroad Company, on Front Street; thence southerly, crossing the Fitchburg passenger tracks at right angles to a point four feet distant south of the south rail of south passenger track; thence westerly on a curved line parallel with the south rail of the south passenger track, and four feet distant therefrom to the south-easterly line of Austin Street in Charlestown. And if the Eastern Railroad Company shall so fake the said property of the Fitchburg Railroad Company, then the Fitchburg Railroad Company shall take or purchase all the like property of the Eastern Railroad Company lying between the crossing of the Eastern and Fitchburg Railroads and Causeway Street in Boston, except the parcel of land to be taken by the Boston and Maine Railroad, as hereinafter provided; and in case of the taking or exchange of the tracks and property herein before described, or any part thereof, the said Fitchburg Railroad Company shall locate and construct such tracks and bridge structures on the westerly side of the present line of the Eastern Railroad as may be necessary to connect its railroad and tracks with the tracks and property so purchased or taken by it; and shall not thereafter cross either said Eastern Railroad or said Boston and Maine Railroad except for freight purposes.