394 H. S. WILLIAMS CORRELATION PROBLEMS 



the sediments we also draw definite inferences as to nearness or distance 

 from the origin of the materials. 



The presence of salt and gypsum, uniformity of fine-grained sedi- 

 ments, with even lamination, ripple-marks, and cross-bedding, each has 

 its interpretation based on the known conditions in modern oceans under 

 which these phenomena arise. 



In these various inferences we are fairly safe because we have the 

 actual relationship of living faunas to conditions now in existence to fall 

 back on, and we can correct our hypotheses by closer observation of exist- 

 ing conditions. 



The difficulties arise when we attempt to draw conclusions on pre- 

 sumptions which are incapable of direct proof from any direct observa- 

 tion. 



For instance, in the case before us the sequence of formations and 

 their contained faunas in the Eastport Quadrangle area bears a very close 

 resemblance to the sequence of sediments and faunas recorded in the 

 Silurian district of England. In both cases there is the gradual change 

 from pure marine sediments, with abundance of a great variety of ma- 

 rine invertebrates, through beds in which the types of life we consider 

 purely marine become rare, and the species that do appear are more 

 closely related to brackish-water species, and closing with the dropping 

 out of all the Brachiopocls except Lingulas, with traces of fish remains 

 and frequent evidence of shallow conditions, such as ripple and wave 

 marks, ending abruptly in a definite line of unconformity, the overlying 

 beds being Upper Devonian instead of Silurian. 



In the British section the same order of events is indicated, and the 

 several stages in the two series are tied together by faunas carrying sev- 

 eral identical species. Both of them indicate a gradual uplifting of the 

 continental mass, the shallowing of the water, and the final protrusion 

 of the surface above the sealevel, making land where for a long period of 

 time marine conditions had prevailed. 



The temptation in this, as in the first case, is to infer that the several 

 geologic events on the two sides of the present Atlantic Ocean were con- 

 temporaneous in this Silurian period of time. 



Let us examine the hypotheses on which such a conclusion rests. 



First, we have to assume that the identity of species in the separate 

 faunas indicates contemporaneity for the several formations in which 

 they lie. 



In the discussion of the Edmunds fauna it was discovered that a ma- 

 jority of the species which can be regarded as identical with transatlantic 



