  New geometric objects on null thin layers are introduced and their importance
for crossing null-like shells are discussed. The Barrab\`es--Israel equations
are represented in a new geometric form and they split into decoupled system of
equations for two different geometric objects: tensor density ${\bf G}^a{_b}$
and vector field $I$. Continuity properties of these objects through a crossing
sphere are proved. In the case of spherical symmetry Dray--t'Hooft--Redmount
formula results from continuity property of the corresponding object.
