In Gaume, the term "crons" (or "cranières") refers to the petrifying limestone springs and the limestone tuff massifs thus formed. The site now appears as a steeply sloping clearing facing south-southeast and traversed by a stream of crystal-clear water. The vegetation and ecological conditions are remarkably diverse: calcareous grasslands, alkaline marshes dominated by Molinia, dry and wet rock slabs, sedge meadows with sedge, buckthorn willow, thermophilic proforest ridges, etc. This environment is a NATURA 2000 priority habitat in the European Union. The wild columbine, with its blue flowers, blooms here in spring.
The fauna is also remarkable: the site, for example, is a favorite biotope of a rare dragonfly, the bidentate cordulegastre, whose larvae develop in the thin streams of water.
The Haie de Han de Saint-Léger Cron Reserve was created thanks to the Municipality of Saint-Léger making available two plots of land located within its forest property (agreement of November 8, 2004): the eastern cron here and the western cron, some 350 m downstream.
The formation of the crons is linked to the precipitation of dissolved limestone in the water from springs gushing upstream at an impermeable marl bank. The springs are an outlet for rainwater, which infiltrates through the sandy limestone layers of Orval and becomes saturated with calcium. In the open air, the dissolved limestone precipitates due to the heating promoted by the topography of the area (a sunny slope) and the growth of mosses. The precipitation eventually produces a rock mass, gradually causing the stream to spread and shift. Areas of so-called active cron (current deposits) and dry, non-irrigated slabs (senile stage of cron) coexist.
Calcareous tuff, also called travertine, is a hard and light rock that has had various uses in the past as a construction material (road conduits, door frames, etc.) but also as a steelmaking flux (limestone) during the forging era.