In the mountains, also in our Alps, in detrital screes at higher altitudes, it usually can be observed that part of the debris seems to flow in large tongues along the mountain sides and canyons. These are the “rock glaciers”: at times they are small masses characterized by concentric wrinkles, at times they are real flows similar to ice tongues, and like the latter they move, descending slowly toward the valley, from which the old name of “active rock glaciers” was given. If we study the internal structure, the presence of ice cementing the debris can be seen: it is because of an ice nucleus that the rock glaciers are able to flow, behaving more or less like small “black” glaciers. Many rock glaciers were formed in recent times due to the formation of ice within the fields of debris, however many others seem to be an evolution of old glaciers of which they apparently represent the relics. It is evident how the latter are greatly important in order to study the glaciers of the past.