The study of information cascade in multiplex networks where agents are connected by multiple linking types has received increasing interest. Comparing with the cascade in simplex networks, a noticeable characteristic of the cascade in multiplex networks is that information may be spread between multiple layers. Here, we focus on the cross-layers cascade which helps clarify two opposite opinions about the information cascade in multiplex networks: multiplexity can speed up or slow down information cascade. Two features of cross-layers cascade are proposed: the mapping relationship provides cross-layers paths; the vertical transfer coefficient quantifies the influences of agent varied in multiple layers. After generalizing the linear threshold model to multiplex networks, preconditions and reasons of seemingly paradoxical phenomena are discussed using three representative case studies and extensive simulations. It is found that the slow-down phenomenon emerges due to the obstruction of...