FIG. 8. — A in The Sarmatian (middle Miocene) "petrified forest" of Gramada (NW Bulgaria): role of the calcareous crusts

FIG. 8. — A, Synthetic diagram of the constitution of the cylinders: 1, GR1, base with the Mactra limestone; 2, GR2, very compact micritic thin layer; 3, GR3, grooved limestone layer; 4, GR4, main mass made up of concentric layers; 5, GR5, dome-shaped top; 6, GR6, central cavity; B, C, details of the cylinders showing the elements 1 to 4; D, detail of the elements 2 to 4; E, detail of the element 3 showing the grooved external appearance; F, longitudinal section of a cylinder showing the concentric layers (4) around the central cavity (6); G, cross section of a cylinder showing the filled central cavity and the different concentric layers (4). Scale bars: B-E, 10 cm; F, G, the hammer gives the scale.