MISSISSIPPIAN LIMESTONE 



;29 



of limestone, there are pitted and frosted sand grains. It is suggested 

 that these isolated grains were dropped by the wind on soft mnd at a time 

 when it was temporarily exposed to the air. Interbedded with some of 

 the sun-cracked strata there are argillaceous breccias in which the angular 

 fragments are chips of hardened mud. These may well be broken pieces 

 of the curled plates which are usually produced in the making of tension 

 cracks in mud. On some of the layers of muddy limestone there are im- 

 pressions of the faces and corners of cubes, which may be ascribed to the 

 temporary formation of salt crystals which were later dissolved. 



The precise mode of deposition of such a deposit is open to question. 

 The facts above stated seem to imply that the sediments were deposited 

 in shallow-water bodies and streams on land. The requisite conditions 

 are probably supplied today on the surfaces of large deltas of flat gradient 

 in regions which are either generally or seasonally arid. 



These Mississippian shales seem to have a fairly wide distribution in 

 the Wasatch Mountains. They are represented in Ogden Canyon by 

 physically similar beds, in which the red color is largely replaced by buff 

 and gra}^ In that locality one of the beds has also yielded a few brachio- 

 pods and jointed fucoidal fossils of problematical nature. 



On the west slope of Mount Morgan reddish shales with mud breccias 

 were noted in the Mississippian succession. There seems to be a repre- 

 sentative also along the crest of the Wasatch range southwest of Wells- 

 ville. 



TEE RED BEDS NEAR MORGAN 



In the upper canyon of Weber River the conspicuous Weber quartzite is 

 separated from the dark Mississippian limestones by a formation of red 

 sandstone and shale with intercalated thin limestones, having a total 

 thickness of about 500 to 2,000 feet. This formation was noted by the 

 geologists of the Survey of the 40th Parallel, but not named. Weeks, in 

 an unpublished manuscript on the geology of northeastern Utah and ad- 

 jacent regions, calls it the "Morgan formation," and in the present paper 

 that name is adopted. The prevailing rock in the Morgan formation is 

 earthy sandstone, which is relatively soft. Fresh surfaces are generally 

 white or pink, but on exposure the rock turns brick red. Some beds are 

 distinctly shaly, and here and there thin layers of gray limestone with a 

 few fossils are interbedded with the series. The Morgan formation 

 passes upward through alternate gray shales, limestones, and sandstones 

 into the more or less calcareous base of the Weber quartzite. In this 

 transitional zone there are a few fossils — chiefly Lingulas and Discinoids. 

 The lower limit of the formation is sharp, for the earthy red sandstones 



