I was studying on the location of the Garden of Eden today, and I noticed the you said the Bible list four rivers Pishon, Gihon, Euphrates, and the Tigris? I don't believe that the Bible list the Tigris. I believe the last river is listed as Hiddekel which is found in Genesis 2:10-14.
"The name of the third river is Hiddekel; it is the one which goes toward the east of Assyria. The fourth river is the Euphrates" (Genesis 2:14 NKJV).
"The name of the third river is Tigris; it flows east of Assyria. And the fourth river is the Euphrates" (Genesis 2:14 NASB95).
Hiddekel is another name for the Tigris, as is seen in Daniel 10:4, "Now on the twenty-fourth day of the first month, as I was by the side of the great river, that is, the Tigris." The same word appears in both Genesis 2:14 and Daniel 10:4. Hiddekel is the transliteration of the Hebrew name for the river and Tigris is the translation of the word.