Editing Tuff (section)

===Folding and metamorphism===
[[File:Servian Wall-Termini Station.jpg|thumb|upright|Remains of the ancient [[Servian Walls]] in Rome, made of tuff blocks]]
[[File:Petrie Bight Retaining Wall, Queen Street, Brisbane 03.jpg|thumb|right|19th century embankment wall built of [[Brisbane tuff]], [[Brisbane|City of Brisbane]]]]
In course of time, changes other than weathering may overtake tuff deposits. Sometimes, they are involved in folding and become [[Shear (geology)|sheared]] and [[Cleavage (geology)|cleaved]]. Many of the green [[slate]]s of the English [[Geology of the Lake District|Lake District]] are finely cleaved ashes. In [[Charnwood Forest]] also, the tuffs are slaty and cleaved. The green color is due to the large development of chlorite. Among the crystalline [[schist]]s of many regions, green beds or green schists occur, which consist of quartz, hornblende, chlorite or biotite, [[iron oxide]]s, feldspar, etc., and are probably recrystallized or [[Metamorphism|metamorphosed]] tuffs. They often accompany masses of epidiorite and hornblende – schists which are the corresponding lavas and [[Sill (geology)|sill]]s. Some chlorite-schists also are probably altered beds of volcanic tuff. The "Schalsteins" of [[Devon]] and Germany include many cleaved and partly recrystallized ash-beds, some of which still retain their fragmental structure, though their lapilli are flattened and drawn out. Their steam cavities are usually filled with calcite, but sometimes with quartz. The more completely altered forms of these rocks are platy, green chloritic schists; in these, however, structures indicating their original volcanic nature only sparingly occur. These are intermediate stages between cleaved tuffs and crystalline schists.<ref name=EB1911/>