Water trickling through the discontinuities of granitic massifs causes a slow chemical and physical weathering of the rock related to biological activity. The weathered materials are first eroded and later deposited in either the same fissures or the water output of fissures. The formed deposits are considered speleothems due to their morphology, genesis and association with rock fissure systems. They are comparable to their congeners in karstic systems s.s. though they are always smaller in size and volume. Speleothems of granite caves are a suitable microenvironment for the settlement and development of microorganisms as bacteria, fungi, algae, diatoms, polychetes, mites, etc., which at least develop part, if not all, of their vital cycle in the speleothem. The biological activity is responsible for the formation of the speleothem because it promotes the weathering of the rock contributing to the generation of new minerals (pigotite, evansite-bolivarite, opal-A) which may be called biominerals due to their relationship with the organic activity and also acting as sedimentation trap of the resulting materials.

The Serras of Queixa-Invernadoiro and Gerês-Xurés in the NW of the Iberian Peninsula are two small mountain massifs located at low altitude that were glaciated in the Pleistocene. The prevailing granitic lithology was a problem for mapping glacial forms (in many cases interpreted as banal granite forms) and for the identification of the tills (misunderstood as remains of regolith). A combination of geomorphological techniques (genetic mapping of granite forms and deposits), the micromorphological study of till thin sections and the morphoscopy of quartz grains at the SEM enabled to establish a model of the geomorphological evolution complemented with the chronology by cosmogenic nuclides (21Ne and 10Be) of both glacial systems. The obtained results represent the glacial evolution of the area from circa 250 ka B.P.

The identification and extent of etch surfaces depends primarily on the preservation of regolithic remnants and the coincidence in level of weathering front and surface. The occurrence of bornhardts, corestone boulders, flared slopes, basins, gutters and pitting on covered weathering fronts demonstrates that they can be initiated in the subsurface, and where they are preserved on exposed surfaces, particularly in assemblages of such features, they constitute sound evidence of an etch origin. In some instances the location of the front and hence of the related etch surface is determined by subtle variations in degree of weathering. There is some suggestion that the front advances episodically rather than continuously. L'identification et l'extension des surfaces « gravées » (etch) dépendent, en premier lieu, de la préservation des rémanents régolithiques, mais également de la coïncidence du niveau de la surface et du front d'altération. L'existence de bornhardts, corestone boulders, versants, bassins, ruisseaux et de fosses sur le front érodé recouvert, prouve que ceux-ci peuvent se produire sous la surface et, dans le cas où ils se préservent dans des surfaces exposées, particulièrement dans des assemblages de ces caractéristiques, ceci constitue une évidence de l'origine de ces surfaces « gravées ». Dans certains cas, la localisation du front, et donc de ces surfaces « gravées », est déterminée par des légères variations dans le degré de météorisation. Certains faits suggèrent que le front migre de façon sporadique et non pas continue.