A dry granular material is modelled as a graph of spherical grains linked by purely repulsive contacts. Its stability (jamming) is insured by odd circuits that prevent the grains from rolling on each other. A topological dynamical matrix is associated with the graph. The odd circuits gathered on the largest R-loop are responsible for the high density (independent of the size of the material and of the dimension) of low-energy excitations and for the extended corresponding eigenstates in (disordered) granular matter at the jamming transition.