You have picked up on a very interesting aspect of the first chapter. As more and more boys congregate because of the sound of the conch, the boys suddenly see something in the distance:
Within the diamond haze of the beach something dark was fumbling along. Ralph saw it first, and watched till the intentness of his gaze drew all eyes that way. Then the creature stepped from mirage on to clear sand, and they saw that the darkness was not all shadow but mostly clothing.
What is interesting about this quote is that is foreshadows the role that Jack and his "gang" will play in the novel - notice how the group of boys are compared to a "creature" that is almost snake-like as it winds its way towards the other boys. Clearly Golding seems to be suggesting something dark and dangerous about this "creature", and indeed, the leader of it as well.
Very helpful for Lord of the Flies!!