from the book "THE PRINCIPLES OF MASONIC LAW"
A Treatise on the Constitutional Laws, Usages And Landmarks of Freemasonry
by Dr.Albert Gallatin Mackey, 1856
The Senior and Junior Grand Wardens were originally appointed, like the Deputy, by the Grand Master and are still so appointed in England; but in this country they are universally elected by the Grand Lodge. Their duties do not materially differ from those performed by the corresponding officers in a subordinate lodge. They accompany the Grand Master in his visitations and assume the stations of the Wardens of the lodge visited.
According to the regulations of 1721, the Master of the oldest lodge present was directed to take the chair of the Grand Lodge in the absence of both the Grand Master and Deputy; but this was found to be an interference with the rights of the Grand Wardens and it was therefore subsequently declared that, in the absence of the Grand Master and Deputy, the last former Grand Master or Deputy should preside. But if no Past Grand or Past Deputy Grand Master should be present, then the Senior Grand Warden was to fill the chair and, in his absence, the Junior Grand Warden and lastly, in absence of both these, then the oldest Freemason, [That is, the one who has longest been a Freemason. ] who is the present Master of a lodge. In this country, however, most of the Grand Lodges have altered this regulation and the Wardens succeed according to seniority to the chair of the absent Grand Master and Deputy, in preference to any Past Grand Officer.