Lots of info out there on them, Dave. Here are a couple of the more interesting and less "trippy" stuff:

"The term "ley lines" was coined by Alfred Watkins when explaining his theory that ancient sites around Britain had actually been constructed or formed giving alignments between and across the inhabited landscape of Britain. The sites mentioned include Stone Circles, Standing Stones, Long Barrows, Cairns, Burial Mounds and Churches. In 1921 Watkins had an idea about alignments and set about noting and measuring these sites to help support his theory. His first book entitled, "Early British Trackways" was published in 1922 and was the result of a lecture he had given the previous year. After this he continued to pursue his study of the alignment theory. In 1925 he published what is said to be his main book entitled, "The Old Straight Track", later books were "The Ley Hunters Manual" (1927) and the "Archaic Tracks Around Cambridge" (1932). Shortly after the publishing of the Old Straight Track, The Straight Track Postal Portfolio club was formed enable people to exchange and circulate information, including viewpoints and photographs, with each other. Major F.C. Taylor in the 1930's was the secretary, but the deaths of Alfred Watkins and Major Taylor and the advent of the Second World War meant that the club closed. Luckily a handful of people kept the interest alive right through to the 1960's when a new cycle of theories emerged.

It is said that the word "Ley" comes from the Saxon word for cleared glade. Paul Devereux and Ian Thompson, in their book, The Ley Guide, quote from the Concise Oxford English Dictionary that the word "ley" can be linked to "lea" meaning a "tracked of open ground." Watkins believed that the image of the actual ley surveyors/designers can be seen by looking at the chalk figure known as "The Long Man of Wilmington," located in Sussex. In 1974 these types of design in the Southern parts of Britain have been linked to the markings on the pampa/ground close to Nasca, Peru, by Maria Reiche a German expert."

AND:

Ley Lines

"Ley lines, or Leys, are alignments of ancient sites stretching across the landscape. Ancient sites or holy places may be situated in a straight line ranging from one or two to several miles in length. A ley may be identified simply by an aligned placing of marker sites, or it might be visible on the ground for all or part of its length by the remnants of an old straight track.

Ley Lines were 're-discovered' on 30 June 1921 by Alfred Watkins (1855-1935), a locally well-known and respected Herefordshire businessman, who while looking at a map for features of interest noticed a straight line that passed over hill tops through various points of interest, all of which were ancient. At the time of his discovery, Watkins had no theory about alignments but on that June afternoon saw "in a flash" a whole pattern of lines stretching across the landscape. Four years later, in 1925, he described his vision in a book he titled The Old Straight Track:

"Imagine a fairy chain stretched from mountain peak to mountain peak, as far as the eye could reach, and paid out until it reached the 'high places' of the earth at a number of ridges, banks, and knowls. Then visualise a mound, circular earthwork, or clump of trees, planted on these high points, and in low points in the valley other mounds ringed around with water to be seen from a distance. Then great standing stones brought to mark the way at intervals, and on a bank leading up to a mountain ridge or down to a ford the track cut deep so as to form a guiding notch on the skyline as you come up.... Here and there, at two ends of the way, a beacon fire used to lay out the track. With ponds dug on the line, or streams banked up into 'flashes' to form reflecting points on the beacon track so that it might be checked when at least once a year the beacon was fired on the traditional day. All these works exactly on the sighting line."

Watkins surmised that these straight tracks, or ley lines as he called them at first, were the remnants of prehistoric trading routes. He went on to associate ley lines with the Greek god Hermes (the Roman Mercury, the Norse Woden) who was the god of communication and of boundaries, the winged messenger, and the guide to travellers on unknown paths. Watkins identified Hermes-Mercury with the chief god of the Druids and argued that:

"A Celtic god, Tout, or in its Romanised form Toutates, is supposed to be what Caesar referred to, and this name has been found on a Romano-British altar. It is a fact that sighting mounds called Tot, Toot, Tout, Tute and Twt abound all over the Kingdom, and the root is probably Celtic... The fact that such mounds are mark-points on trackways strengthen the link..."

The identification of leys as ancient traders' routes was as far as Watkins was prepared to go, despite the fact that numerous ley lines travelled up prohibitively steep hillsides. Speculation as to their meaning and purpose continued after Watkins' death in 1935.

According to Paul Devereux, it was the occultist Dion Fortune in her 1936 novel The Goat-Foot God (republished in 1971 by S. Weiser, New York, and in 1989 by Aquarian Press, Northamptonshire) who invented the idea that ley lines were "lines of power" linking prehistoric sites. A few years later, it was suggested that ley lines followed lines cosmic energy in the Earth and could be detected using dowsing rods. In the 1960s, ley lines, or "leys" as they were now called, became linked with UFO sightings.

In 1969, ley lines were taken up by John Michell, in his seminal book The View Over Atlantis, who discussed them within the context of geomancy. By 1974, ley lines and geomancy, plus other esoteric subjects having to do with the Earth, were collected under the umbrella term of "Earth Mysteries." "