In this note, which results from a paper published in France, the author defines the “karst system” formed by several successive levels, at the heart of a limestone mass: joints of surface feeding, vertical chimneys, galleries which are alternatively dry and full of water according to the season, a network of continually drowned clefts. He then studies modifications in this system resulting from internal causes, corrosion, filling and sedimentation, concretion. Then he shows how this evolution of the karst system may be modified by general conditions: geology, tectonics, geography with the losses, resurgences and the role of surface formations. The deepening of the river level may create a structure of differing levels in the various karst system, but their positioning is always slower than the streams erosion and it comes about later. In any case, the caves in a dried karst system undergo an evolution on their own. Finally, the author gives the definition of the terms used to explain the evolution in the karst system: “embryonic galleries” in the network of clefts, “young galleries” in the zone which is alternately wet and dry, “mature galleries” where the concretion and the erosion are balanced, “old galleries” where the concretion is becoming more and more important, “dead galleries” where the cave is completely filled by the deposits and concretions. This classification will easily replace the inexact terms of “active galleries” and “fossilized galleries” which are too vague and lead to confusion.