Introduction

Abstract

Sediments are formed of materials deposited episodically from water, air and ice, as well as soils, coals and volcanic detritus. Compaction, cementation and burial processes lithify loose sediments into sedimentary rocks and occasionally mask the character of the original deposit. Fortunately, many lithified rocks possess qualities so similar to those of modern deposits that the conditions under which they formed can be determined with some certainty. When fossil remains and traces exist, such determinations are greatly facilitated. On the other hand, there are sedimentary rocks, such as banded iron-formations and chalks, which can be described accurately but which still defy completely satisfactory genetic interpretation, because there are no clear modern equivalents.