324 STUDIES FOR STUDENTS 



hended all of the essential factors which lead to a result. This is 

 especially true of geological science, where the field of the unknown 

 is so great, and where, for example, the past few years have brought 

 forth facts in regard to Cambrian and Permian glaciation which have 

 overthrown previous confident deductions in regard to the nature of 

 Paleozoic climates. Deductive conclusions, especially, therefore, 

 until confirmed by detailed study, should be offered as suggestive, 

 rather than conclusive; to be tested by investigation before being 

 finally accepted ; but on that account they are none the less valuable. 

 The following article must therefore, as previously stated, be 

 divided into two portions: first, an inductive study from observed 

 facts as to the general relations of land, seashore, and marine sedi- 

 mentation; and, second, the deductive application of the relation of 

 these to the topographic cycle and to previous time. The last is to 

 be taken as true only in a broad way, and with many possible excep- 

 tions; as suggestive rather than final. 



THE IMPORTANCE OF CORRECT INTERPRETATION 



Stratified deposits may be laid down either upon the land, beneath 

 the sea, or in that transition zone known as the littoral, which by the 

 ebb and flow of tides belongs alternately to the sea and the land. It is 

 of fundamental importance in stratigraphic geology that land and sea 

 deposits should be sharply distinguished from each other, as may be 

 seen from the consequences which follow in attempting to outline the 

 ancient geographies. On the one hand, if the formation is considered 

 marine, it implies a submerged attitude to the land, a spread of ocean 

 waters, a home suitable for the development of marine faunas, a barrier 

 between lands — separating into distinct provinces the neighboring 

 terrestrial faunas. On the other hand, if the formation is considered 

 to be of terrestrial origin, precisely the opposite conditions are implied, 

 the region now excluding the life of the ocean and serving for the sup- 

 port of land-dwelling types, and possibly offering means of communi- 

 cation between otherwise separated lands. The third alternative is 

 to consider the deposits as transitional and belonging to the littoral 

 zone, in which case the life is predominantly related to the sea, though 

 invaded between tides by life from the land. 



As oceanic, transitional, or continental, the region must be repre- 



