524 E. BLACKWELDER GEOLOGY OF WASATCH MOUNTAINS, UTAH 



glomerate in which the pebbles consist of qnartz and qnartzite well 

 rounded and moderately well assorted. Many of the sandy beds are 

 prominently cross-bedded, the cross-bedding having a relatively small 

 amplitude. On the bedding planes ripple-marks, generally of the long 

 parallel type, are of common occurrence. 



At several horizons in the section, but especially in the lower portion, 

 hard shales and slates are interbedded with the quartzites. The prevail- 

 ing colors of these argillaceous members are dark purplish brown or 

 bright green, but there are some which are distinctly black and others 

 rich maroon. The purplish, maroon, and green beds are composed of 

 poorly assorted material, consisting of clay and sand, with abundant mica 

 flakes. Tension cracks have been found in them at several points and ap- 

 pear to be relatively common. About 2 miles northwest of the village of 

 Liberty, in Weber County, there is a small mass of coal-black slate with 

 imbedded pyrite crystals. The relations of this member are not observ- 

 able, but it is evidently a part of the Algonkian sequence. 



Excepting a few thin beds of brown dolomite interleaved with the 

 slates northeast of Willard, no beds of limestone have been observed any- 

 where in the section. Lil^ewise no fossils have been found, although 

 considerable time was spent in search for them in beds of shale which 

 have suffered little deformation and still less metamorphism and which 

 preserve unmarred their original stratification. Walcott mentions the 

 fact that the most promising shale beds in the Big Cottonwood Canyon 

 section yielded no fossils to a painstaking search. 



The significant characteristics of the Algonkian system in this region 

 may then be summarized as follows : It consists of alternating beds of 

 quartzite, slate, and conglomerate, which are variable from place to place ; 

 cross-bedding, ripple-marks, and mud cracks are prevalent. The mate- 

 rials are not well assorted, and in the sandy beds the prevailing colors are 

 yellow, gray, and red, while purple, maroon, and green predominate in 

 the shaly layers. There is apparently a general lack of limestone and of 

 fossils. 



Sedimentary deposits having a thickness of many thousands of feet 

 have generally been assumed to be of marine origin. It is now well 

 recognized, however, that thickness has no such necessary implication. 

 Fluviatile deposits, such as the Siwalik formation of India and the Cali- 

 fornia Valley sediments, are known to have great depth. In the Algon- 

 kian of the Wasatch region the absence of limestone from so great a 

 thickness of rocks and the dearth of fossils in beds so little altered is in 

 itself significant. The cross-bedding which is a characteristic feature 

 of the strata at many horizons is indicative of shifting currents. The 



