ALGONKIAN QUARTZITE-SLATE SERIES 525 



regularity of dip and the small amplitude of the cross-bedded structures 

 implies currents moving in a single general direction, and currents of 

 water rather than of wind. The uniformity of the cross-bedding in 

 stratum after stratum may be taken to mean a constancy of conditions 

 scarcely to be expected on a sinking sea bottom. The beds of conglom- 

 erate locally interstra titled with sandstone show that the currents were 

 alternately stronger and weaker at the same point. The ripple-marks 

 are of less significance than some other features, although they indicate 

 shallow water and are in harmony with the testimony of the other feat- 

 ures. BarrelP^ has called attention to the fact that tension cracks are 

 best developed on muddy flats bordering streams or lakes subject to con- 

 siderable seasonal changes of climate. While it is possible to have them 

 formed along tidal flats, such situations are probably much less favorable 

 to their preservation. The imperfect assortment of the materials ap- 

 pears to indicate that the sediments were deposited rapidly, little time 

 being given for that complete sifting of fine from coarse debris which is 

 characteristic of the work of waves upon an open beach. These consider- 

 ations lead to the inference that most of the Algonkian system in the 

 Wasatch region is a product of deposition on land rather than in the sea, 

 by means of rivers rather than in lakes or by winds, and at a geologically 

 rapid rather than at a slow rate. 



The existence of tension cracks is already referred to as indicating 

 seasons of relative dryness. The dearth of black, gray, and olive green 

 sediments and the prevalence of red, purple, and brown colors in the 

 greater part of the section may also be interpreted to mean that the 

 sediments were laid down under conditions which were oxidizing rather 

 than deoxidizing. This in turn points to a scarcity of vegetation and to 

 a relatively warm, dry climate during most of the year. The absence of 

 fossils would be readily explainable upon this hypothesis, even if the 

 formation were not so old as to have preceded the existence of preservable 

 organisms. 



In this connection attention may be called to the fact that many of the 

 features of the Wasatch Algonkian have been observed in strata probably 

 of the same age in the Grand Canyon region on the south, and in Idaho, 

 Montana, and Canada on the north. Whatever interpretation applies to 

 the one should apply to the homologous parts of the others, indicating 

 that the conditions which favored such deposits were widespread in the 

 West at the time. BarrelP^ argues for the continental origin of a large 



" Joseph Barrel! : Geological importance of sedimentation. Journal of Geology, vol. 

 xlv, 1906, p. 552. 



" Op. cit., pp. 553-568. 



