  We denote by Conc(A) the semilattice of compact congruences of an algebra A.
Given a variety V of algebras, we denote by Conc(V) the class of all
semilattices isomorphic to Conc(A) for some A in V. Given varieties V1 and V2
varieties of algebras, the critical point of V1 under V2, denote by crit(V1;V2)
is the smalest cardinality of a semilattice in Conc(V1) but not in Conc(V2).
Given a finitely generated variety V of modular lattices, we obtain an integer
l, depending of V, such that crit(V;Var(Sub F^n)) is at least aleph_2 for any n
> 1 and any field F. In a second part, we prove that crit(Var(Mn);Var(Sub
F^3))=aleph_2, for any finite field F and any integer n such that 1+card F< n.
Similarly crit(Var(Sub F^3);Var(Sub K^3))=aleph_2, for all finite fields F and
K such that card F>card K.
