What is Alluvio Maris?

Legal Definition
Lat In the Civil and old English law. The washing up of the sea; formation of soli or land from' the sea; maritime increase. Hale, Anal. § 8. "Alluvio maris is an increase of the land adjoining, by the projection of the sea, casting up and adding sand and slubb to the adjoining land, whereby it is increased, and for the most part by insensible degrees." Hale, de Jure Mar. pt. 1, c. 6.
-- Black's Law Dictionary