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This contribution tries to verify the hypothesis on the initiation and propagation of the cross crack by means of behaviour in tensile tests with the con-cast slab of the same basic chemical composition in the range of temperature moving from 25°C to 1450°C. The tensile tests were made on 18 test bars at suitably chosen temperature differences and gradually led to the tension ruptures of the bars under exactly defined conditions. Simultaneously, the roughness of the resultant rupture surface depending upon the temperature was studied in detail. Thus relations between the roughness of the rupture surface, tension force, work to rupture and contraction with the test bars at the given range of temperature were determined. On the basis of the comparison of the rupture surfaces of cross cracks found in the study and the rupture surfaces obtained at the given interval of test temperatures in the course of this study, properties of material of the slab affected by the cross crack and its most probable behaviour during solidification and cooling were then evaluated by analogy. In this way it was possible to specify and verify the mechanism of cross crack initiation and propagation and to assess the temperature interval, within which the initiation was the most probable.