A crossflow wall for a gas stream has baffle elements which form inlet ducts, which narrow in the inflow direction, and end in a steadying bead. Coaxially to the baffle elements, concave impingement surfaces are arranged which are staggered relative to the baffle elements and are curved at a distance around the steadying bead thereof, so that they deflect the gas stream to the rear of the baffle elements. The baffle elements and impingement surfaces are of at least approximately rotationally symmetrical shape and are arranged with pairs of them having parallel axes. Between the impingement surfaces, outlet ducts are left free, through which the gas stream leaves at least approximately parallel to the inflow direction. The heavy foreign matter particles accumulating in the vicinity of the impingement surface are collected in the peripheral edge of the impingement surface by a collecting channel, are passed into a collecting chamber and extracted.