114 ANNALS NEW YORK ACADEMY OF SCIENCES 



fauna, a middle sandstone and shale, apparently barren of fossils, and an 

 upper limestone series which is very fossiliferous. These beds are well 

 exposed in Big Cottonwood Canyon at the northern end of the Eeade and 

 Benson ridge which separates South Fork from Day's Fork. At Green's 

 Hill in South Fork, the lower limestone can be traced across the canyon 

 from east to west. From the cliff which rises on the west, the following 

 forms were obtained : 



Productus semireticulatus 

 Productus cora 

 Derby a sp. 

 Hapsyphyllum sp. 



The sandstone and shale which overlie this limestone member were 

 not well exposed within the district, usually forming the bottom of 

 gulches because of their poorer resisting qualities to weathering and 

 being largely covered with talus and soil. No fossils were found in them, 

 but they may have been overlooked because of poor exposures. The 

 sandstone, where seen, is composed of much angular material giving it 

 the aspect of a breccia. The prevailing color of the sandstone is light 

 yellow, straw color, while the shale which overlies it has a reddish tint. 

 It is an interesting fact that Blackwelder has noted a similar occurrence 

 sixty miles to the north, in Ogden Canyon, and several localities there- 

 abouts. The exposures there are apparently better and have been care- 

 fully described. Lavender and maroon shales with abundant sun-cracks 

 filled with mud and sand and the same brecciated appearance are noted. 

 From these and other characters, a continental origin is suggested, the 

 necessary conditions being found on the surface of deltas of flat gradient 

 in regions which are either generally or seasonably arid. The presence 

 of this non-marine member within the Mississippian was not noted until 

 it was discovered in Ogden Canyon by Blackwelder^^ in 1910, and its 

 recognition in Big Cottonwood Canyon by the writer gives it a much 

 wider distribution and importance as a stratigraphic unit. It will, no 

 doubt, partly account for the limited development of the Mississippian 

 rocks in the Wasatch Mountains. In this connection, the unconformity 

 at the top of the over-lying thin-bedded limestones is of great importance. 

 As will be shown, this represents a great interval of time during which 

 much of the Upper Mississippian must have been removed by erosion. 

 From the fossiliferous portion of the limestone immediately below this 

 break, the following forms were obtained : 



23 E. Blackweldkr : "New Light on the Geology of Wasatch Mountains, Utah," Bull, 

 G. S. A., Vol. 21, pp. 528-529. 1910. 



