How was Hashem Go'er b'Yam?
Radak: It was via the wind, which took the sea [water] until it made [the ground] dry - "Go'er b'Yam va'Yabeshehu" (Nachum 1:4).
What are "Tehomos ba'Midbar"?
Rashi: It is Yam Suf, which is in the Midbar - "Sagar Aleihem ha'Midbar" (Shemos 14:13), "Derech Sheloshes Yamim
Why didn't Rashi simply cite "Derech ha'Midbar Yam Suf" (Shemos 13:18) or "va'Ya'avru b'Soch ha'Yam ha'Midbarah" (Bamidbar 33:8)? Perhaps he did, and scribes erred. The continuation of the latter verse is "[va'Yelchu] Derech Sheloshes Yamim b'Midbar Esam." Texts in which Rashi cites Bamidbar 10:3 are overtly wrong. (PF)
Rashi (114:2, from Pirkei d'R. Eliezer 42, Shocher Tov 76:2): Nachshon jumped to descend into the sea. (Perhaps Hashem lifted the floor after he jumped. - PF)
