A scenario of the galactic halo formation through mergers of fragments is considered. In the framework of the scenario sets of the fragments are obtained from the observed halo metallicity distribution functions for the Milky Way and some other galaxies. Our results allow us to make the following suggestions: 1) in the Galaxy the halo field star formation occured in fragments evolved as a closed system; 2) in the Galaxy the formation of the halo field stars can be associated with the halo globular cluster formation; 3) the formation of the bulk of the halo field stars for M31 and NGC 5128, perhaps, is not connected with the formation of the halo globular clusters in these galaxies.