Within the London approximation, we show that in anisotropic, strongly
type II superconducting slabs two ''species'' of vortices can coexist
simultaneously when the external magnetic field is applied at an angl
e with respect to the crystal principal axes. Simple thermodynamic arg
uments are used to prove that the appropriate thermodynamic potential
is minimum when some of the vortices lie parallel to the c axis while
others lie at an angle with respect to the c axis.