Originally Posted by 'Geologie der Schweiz' by B. Stüder, Bern/Zürich 1851
The principal mountain range of the Apennines mainly differs from its southern continuation in the Abruzzi by the more prominent and more abundant appearance of the Macigno and in the sporadic presence serpentine.
The Macigno, or Pietra serena, or Pietra forte of Florence, is a solid sandstone, internally mostly dark blueish, externally brownish gray, consisting of quartz grains and white mica flakes held together by cement marl, partly so fine-grained that the grains and mica specks are only recognizable by their sheen; and partly rougher grained, partly passing over into 'Cicerchina' a conglomerate of white, and also black and red pebbles. The fine-grained stone not infrequently contains scattered pebbles too, and more often still large or small fragments of black slate.
The layers are multiple feet to a yard thick, though often only so thin that the stone becomes sandstone slate, the strata of which are barely a line thick and covered with white mica lamellae. Thicker layers are often separated by an intermediate layer of marl that covers the surface and sometimes draws knobby figures, looking like roots, worms, footprints. Thicker layers are divided into polyhedral chunks by crevices, usually filled with calcite and perpendicular to the stratification. Brown, or charred plant debris, with no definite form and structure, often as a finely divided dust, or covering the layers' surfaces in denser batches, are the only organic remains that to date have been found in the Macigno.
