The present paper contains an approach to systematize the study of the State of Paraná coastal plains, in the southern part of Brazil. It contains in general some geographical and geological data, documented by maps, sketches and photographs. In the initial stage the coastal plain represents a marine ingression, caused by faulting. This ingression penetrated the valleys of a not yet determinated geological landscape. Ended the movement of deeping by faulting begins the epirogenic ascension and building of the barriers and beach ridges. An intensive sedimentation caused the lagoons and bays obstruction. This work refers mainly to t33 he sedimentary formations and the coastal plains is classified in the following way for the study in consideration to the morphology and origin: Marine sedimentation - shore, barrier and beach ridge; Intermediary sedimentation - mangrove swamps, mud and sand banks and mangrovito; Continental sedimentation - dunes and terrestrial alluvion. There are also presented some data about the rocky coast and vegetation.

In this paper the author studies some sand samples from the coastal plain and beaches of south Brazil. He modifies the former opinion about the origin of the hard and brown layers of sand, before named by him mangrovito. He suggests the action of the underground water rich in organic matter as being responsible for the hardening of the ancient shore sands.