A (Natural Method) session is composed of exercises belonging to the ten fundamental groups: walking, running, jumping, quadrupedal movement, climbing, equilibrium (balancing), throwing, lifting, defending and swimming.
A training session consists, then, of exercises in an outdoor environment - a course of greater or lesser distance (a few hundred meters to several kilometers), during which, one walks, one runs, one jumps, one progresses quadrupedally, one climbs, one walks in unstable balance, one raises and one carries, one throws, one fights and one swims.
Erwan, in his MovNat philosophy, has taken this basic approach and developed it, adding some of his own ideas.
The American Parkour site has just posted a fascinating document.
Pilou, a Primal Fitness and DC local who grew up in France has found, translated, then made available for us, Georges Herbert's "Methode Naturelle." He writes:The PDF is here
"For the past few months, I have been reading and experimenting with Georges Hébert's physical education guide from 1912 that I found digitized on Google Books. I think most traceurs have heard something about Georges Hébert, the "Natural Method" and how it somehow relates to Parkour. Thanks to that book, I was able to see for myself what it was all about, and I have to admit that I have been very impressed."
Donwload it - it is interesting, even just as an historical document.