It is known that chaotic attractors appear in the driven strongly nonlinear systems as a result of the mechanism of period doubling at system parameters changing such as amplitude or frequency of the excitation. Using the method of complete bifurcation groups allows to identify the different bifurcation groups with an infinite number of unstable periodic regimes, whose existence is a necessary condition for the birth of chaotic attractors. In this paper we consider the topology of the isle type structures, which is the birthplace of chaotic attractors. It is shown that the structure of the isles of this type is, in the plane of two parameters, the closed envelope with a periodic regime nT at the boundary of the shell (near the fold bifurcation) and UPI inside the area. The existence of chaotic attractors in a thin layer of shell on the plane of two parameters, which is a typical topological element of chaotic dynamics in the driven nonlinear oscillations, is shown.