A famous conjecture from Coleman and Oort says that for genus g greater than 0 there do not exist positive dimensional special subvarieties of generically contained in the Torelli locus. Firstly we will give a brief introduction to the characters of this conjecture. Then we will describe how the examples of totally geodesic subvarieties of known so far are obtained as families of Jacobians of Galois coverings , where the genus of is . We will show that all these examples satisfy a sufficient condition that we will explain. Finally, we will see that this condition gives us a bound on .