804 J. BARRELL MEA81 KKMEXTS OF (GEOLOGIC TIME 



cluirnecl np the sediment witlioiit eariying any away. The width of 

 t]]e ribbon represents merely wliat settled from the water on the sub- 

 sidence 01 the storm. During the progress of the storm, sediment was 

 l)eing sconred ont and worked to localities of deeper and quieter water. 

 The development of the bedding planes in this slate and their expansion 

 into ribbons represent, then, a region and a depth where waves gently 

 agitated the bottom, sweeping material along and spreading it out in 

 tlie quieter waters. Ehythmjc intensification of this action resulted in 

 an alternation of fill and scour in which the surface of sedimentation 

 was raised and depressed by changing intensity of wave action and main- 

 tained throughout a marked parallelism distinctive from current action. 



Certain inductions having wide application to beds of marine silts may 

 be drawn from this clear example. The regularity in the succession of 

 the beds and the grouping of these beds into sequences shows a combina- 

 tion of climatic rhythms marked by varying intensity of storms. The 

 sediment was deposited in close accord with wave-base, and the dow^n- 

 scouring probably did not cut out more than half of each deposited bed, 

 since otherwise the remainders would not form such a regular series. 

 After each culmination of intensity continuous deposition, so far as this 

 eyicle is concerned, seems to have occurred, giving rise to the following 

 bed with a definite and constant mixture of mud and fine sand. Con- 

 sidering the fine-grained character of the sediment, the wide area of the 

 formation, and the abundance of carbon, the sediment must have been 

 deposited slowly. The thickness of the beds, ranging from several inches 

 to several feet, indicates, then, a rhythm far too long to be regarded as 

 seasonal. It can not be less than decades or centuries in length. The 

 land lay to the eastward and was presumably low. The denudation rate 

 was consequently slow, and therefore, as a maximum limit, the cycle may 

 represent some thousands of years. The amount of variation in wave 

 intensity to give this rhythm was moderate. Thus we reach the con- 

 clusion that the climate was more uniform than at present, but was 

 affected by regular oscillations comparable to the Bruckner cycle of 35 

 years, but more probably of longer period. Such a regularity in climatic, 

 rhythm suggests as a cause fluctuations in solar energy. In the strata 

 of such ancient formations is locked up, not only a history of the planet, 

 but also the history of the sun as a variable star. 



Some further illustrations of the variety of rhythms, especially those 

 showing in disconformities and diastems, should be given. The first of 

 these, taken up in sequence of age, is a view of a series of cryptozoan beds 

 from the Lower Ordovician (see plate 44, figure 1, photograph of an ex- 

 posure near Allentown, Pennsylvania). The cryptozoan layers show white 



