[Olog-hai]

In Old English, those sounds were written with distinct letters, thorn when unvoiced (Þ, þ) and eth when voiced (Ð, ð). In modern Greek, the unvoiced sound is written with theta (Θ, θ) and the voiced with delta (Δ, δ).

[Verginius Rufus]

Those two letters used in Old English are still used in modern Icelandic.