FIG. 4. — A in The Sarmatian (middle Miocene) "petrified forest" of Gramada (NW Bulgaria): role of the calcareous crusts

FIG. 4. — A, Satellite view of zone 2; the white dots represents the cylinders (the white arrows indicate the place of some cylinders); B-D, Cylinders in natural vertical position; B, Example of cylinder exhibiting a preserved dome shaped in form of "hat"; E, View of the outcrop under the zone 2 (Z2) with horizontal limestone beds indicated by the white arrow; F, Detail of the outcrops directly below the cylinder zone; it displays the oolitic limestone (ool) topped with Mactra limestone (mac); G, Detail of the limestone with accumulations of Mactra. Scale bar: A, 50 m; F, G, the hammer (length: 28 cm) gives the scale.