This was the last annexation of territory from Arlington County. A special provision of the Act[54] establishing the County Manager plan of government, adopted by Arlington in 1930, effective January 1, 1932, prevents the annexation of any _part_ of the County (but permits annexation of the _entire_ County after referendum). In 1938, as a further precaution, the legislative delegation representing Arlington County succeeded in having the General Assembly enact a law[55] which prohibits the annexation of territory from any county which would result in reducing the area of that county to less than 60 square miles of highland. Since Arlington has less than 26 square miles, this Act effectively checks any further such encroachments upon its territory. [54] Acts of Assembly, 1930, Chapter 167; Cf. also, _Code of Virginia, 1950_, Title 15.1, Sec. 692. [55] Acts of Assembly, 1938, Chapter 22; Cf. also, _Code of Virginia, 1950_, Title 15.1, Sec. 1056. Development on both sides of the 1929 boundary line, construction of streets and notably of the Henry G. Shirley Memorial Highway--and especially changes in the channel of Four Mile Run--eventually brought dissatisfaction with that line. In 1962, the Arlington and Alexandria legislative delegations secured enactment by the General Assembly of an Act[56] permitting an adjustment in the boundary to be concluded by mutual agreement between the governing bodies of the County and the City, the agreement to be recorded in the Clerk's Office of both jurisdictions. [56] Acts of Assembly, 1962, Chapter 314. Negotiations began after the area affected had been surveyed and the private property which might be the subject of exchange had been appraised. Impetus was given by the need of Arlington for land in connection with enlargement of the County sewage treatment facilities; this land, although on the North side of Four Mile Run fell in Alexandria. Finally, the Arlington County Board gave approval in principle to a draft proposal on April 10, 1965,[57] and on April 13, 1965, the Alexandria City Council followed suit. A public hearing was held on May 5, 1965, but final action was deferred pending refinement of the proposal. In December 1965, the final agreement was recorded[58] and the transfer of certain publicly owned property approved by the Circuit Court. The net gain to Arlington's area was 167 acres. [57] Arlington County Board Minute Book XXI, p. 54. [58] Alexandria _Deed Book_, 641, p. 188 (December 21, 1965); Arlington _Deed Book_, 1609, p. 453 (December 23, 1965); Arlington _Common Law Order Book_ 85, p. 197. For the description of the new boundary, see Appendix. This procedure for rectifying boundaries between a County and a City is highly unusual in the Virginia experience. _Arlington's Boundary with the District of Columbia_