Negative dyke (i.e. with inside eroded) in the desert, around the center of the Makhtesh Ramon. Fingering structures can be observed on the two sides of the dyke, corresponding to each other. The hydrofracture due to the magma lead to this labyrinthic pattern, frozen on the sides of the hardened sandstone. We sit in the middle of the sandstone, at height, the basalt corresponding to the hardened lava intruding the sandstone (the dyke) has been eroded - we sit on it. Geology field trip during the first topical school of the ITN FlowTrans (flowtrans.digijuice.co.uk/ ), organized by E. Aharonov. Thanks to Gidi Bear who lead us to this fantastic dyke, in Ardon Wadi (Nahal), center of the Makhtesh Ramon, close to Mitspe Ramon, in the Negev. More info: http://eost.unistra.fr/renaud/