A prehistorical archeologist sounds like a 10,000 year old
          scholar who studied archeology.  But, then on other
          days, I think it may be what I am becoming.
 
          Fowler (modern English usage) says that, "The
          differentiation between historic and historical has reached
          the stage at which it may fairly be said that the use of one
          in a sense now generally expressed by the other is a
          definite backsliding.  The ordinary adjective of history is
          historical; historic means memorable, or assured of a place
          in history, now in common use as an epithet for buildings
          worthy of preservation for their beauty or interest;
          historical should not be substuted for it in that sense.
          The only function retained by historic is in the grammarian'
          technical terms historic tenses, moods, sequence, present,
          etc., in which it preserves the notion appropriate to
          narration of the past, expecially in the expression h.
          present, a device for imparting vividness to a narrative
          which is not now so popular with story-tellers as it once
          was.
 
          Although both adjectives are now always aspirated when not
          preceded by the indefinite article, the use of an with them
          lingers curiously."