  Measurements are presented of inclusive charm and beauty cross sections in
e^+p collisions at HERA for values of photon virtuality Q^2 > 150 GeV^2 and of
inelasticity 0.1 < y < 0.7. The charm and beauty fractions are determined using
a method based on the impact parameter, in the transverse plane, of tracks to
the primary vertex, as measured by the H1 vertex detector. The data are divided
into four regions in Q^2 and Bjorken x, and values for the structure functions
F_2^{c\bar{c}} and F_2^{b\bar{b}} are obtained. The results are found to be
compatible with the predictions of perturbative quantum chromodynamics.
