No, these funny mushrooms, made of silica, have not been sculpted by erosion. They were built by living beings, the stromatolites. These microbial colonies are the oldest known terrestrial fomes of view. Living rock tubers? The strange stromatolites in the Tepuis can take on many forms: mushroom shapes, reef scaffolds, velvety surfaces. In contrast to most of their relatives in salt lakes or the deep sea, however, they consist of quartz crystals - and thus provide information about life in early earth-age. In which calcium carbonates were not yet widespread.