Peleg; for in his days was the earth divided. — This may refer to the breaking up of the race of Shem into separate nations, which severally occupied a distinct region; and so, while Joktan took Arabia, and in course of time expelled the Hamites from that country, Asshur, Aram, and Peleg occupied the regions on the north and north-west. But as Peleg, according to the Tôldôth Shem, was born only 101 years after the flood, Noah’s family could scarcely have multiplied in so short a time to as many as 500 people; and Mr. Cyril Graham considers that the name refers to “the first cutting of some of those canals which are found in such numbers between the Tigris and the Euphrates.” This is made more probable by the fact that Peleg in Hebrew means water-course.
Genesis 10:25
25 And unto Eber were born two sons: the name of one was Peleg;g for in his days was the earth divided; and his brother's name was Joktan.