Applying depositional sequence stratigraphic concepts to the interpretation of siliciclastic depositional systems is becoming an increasingly important tool in petroleum geology. After a succession of breakthroughs during the 1970s and 1980s, sequence stratigraphic concepts now have entered a phase of intense application and documentation, especially with regard to successful implementation in the field of petroleum geology. Workers have applied these concepts to a variety of data bases ranging from outcrop to cores to electric logs to multifold seismic data. Clearly, sequence stratigraphic concepts embody not a rigid model or template, but rather a way of looking at geology.

Our understanding of the mechanisms by which organisms fonn minerals has progressed in the past two decades but is still at a rudimentary stage. Any general theory of biomineralization must explain the formation of solid phases from biological fluids in tenns of physical parameters such as supersaturation, ionic strength, pH, surface energies and the character and quantity of active sites. Knowledge of the functions of the organic matrix' in mediating mineral deposition is of basic importance to any understanding of biomineralization..

Most of the land surface of the earth is formed by valley slopes. At a given point on the ground surface it is normally possible to follow the line of maximum slope downwards until a drainage channel is reached; moreover a causal relation between the slope and the channel is apparent. This feature has been little remarked upon, possibly because it is so widespread as to seem part of the natural order. It is nevertheless a fundamental and remarkable feature of the earth’s surface form. <...>