Paul Simon sang, "I am a rock, I am an island."

Explanation

The sentence is a reported speech, and the quotation marks are used to set off the spoken words. In this case, the spoken words are:"I am a rock, I am an island."The comma after "rock" is correctly placed to separate the two independent clauses within the quotation marks. However, the sentence is missing a comma after the first "I" to separate the introductory phrase from the rest of the sentence.The correct punctuation would be:"Paul Simon sang, 'I, am a rock, I am an island.'"The comma after "I" is called a "listing comma" and is used to separate the introductory phrase from the rest of the sentence.