The structural and optical properties of the Ge1- xSnx layers with Sn mole fraction x of about 0.04 and 0.07 grown by molecular beam epitaxy on strain relaxed (001) Ge buffer layers have been investigated. The formation of GeSn solid solutions is proved by the high-resolution X-ray diffraction and micro-Raman investigations. The Ge1 - xSnx layers are found to be partially relaxed, the degree of strain relaxation increases from 8% in the layer with x = 0.04 to about 14% in the layer with x = 0.07. For the Ge and Ge1 - xSnx layers the miscut and tilt angles were calculated and compared with those predicted by Nagai's theory. For the Ge1 - xSnx layer with x = 0.07 an abnormally large tilt of about 0.26 degrees of the epilayer (001) lattice planes with respect to the corresponding substrate planes is found. It is shown also that the epilayer tilt axis is rotated on about 90 degrees with respect to the direction of a substrate miscut. The possible mechanisms of the effect are discussed. (C) 2015 Elsevier B.V. All rights reserved.