North Sea Germanic, also known as Ingvaeonic , is a group of West Germanic languages that were first spoken in what is now northern Germany, the Netherlands, and Denmark. They were also spread to the British Isles in the Migration Period. The languages were Old Frisian, Old English and Old Saxon. They have become other languages since then and spread worldwide, especially the modern English language.
Sources
Bremmer, Rolf H. (2009). An Introduction to Old Frisian. Amsterdam: John Benjamins B.V. . Euler, Wolfram (2013). Das Westgermanische - von der Herausbildung im 3. bis zur Aufgliederung im 7. Jahrhundert - Analyse und Rekonstruktion (West Germanic: from its Emergence in the 3rd up until its Dissolution in the 7th Century CE: Analyses and Reconstruction). 244 p., in German with English summary, London/Berlin 2013, . Maurer, Friedrich (1942) Nordgermanen und Alemannen: Studien zur germanischen und frühdeutschen Sprachgeschichte, Stammes- und Volkskunde, Strasbourg: Hüneburg. Ringe, Donald R. and Taylor, Ann (2014). The Development of Old English - A Linguistic History of English, vol. II, 632p. . Oxford. Sonderegger, Stefan (1979). Grundzüge deutscher Sprachgeschichte. Diachronie des Sprachsystems. Band I: Einführung – Genealogie – Konstanten. Berlin/New York: Walter de Gruyter. . Voyles, Joseph B. (1992). Early Germanic Grammar: Pre-, Proto-, and Post-Germanic. San Diego: Academic Press. .