The Upper Devonian was a period of marine retreat; the crustal disturbances of the Lower Devonian were renewed and great quartz-pebble beaches were formed on the rising shore lines, producing the West Coast Range conglomerates of Tasmania, and the similar rocks to the south-east of Mansfield in Victoria.
A peculiar feature of the hydrography of Tamaulipas is the series of coastal lagoons formed by the building of new beaches across the indentations of the coast.
The sea-face is generally overhanging cliff, but in a few places are sandy beaches and low sandhills.
The coastal plain consists in great part of sandy beaches, detritus formations, and partially submerged areas caused by uplifted beaches and obstructed river channels.
In Rio Grande do Sul, where two large lakes have been created by uplifted sand beaches, the coastal plain widens greatly, and is merged in an extensive open, rolling grassy plain, traversed by ridges of low hills (cuchillas), similar to the neighbouring republic of Uruguay.