WEBER SHALES. 67 



Weber Shales. — Oil the general map of the Mosquito Range, owing to its 

 small scale, it was considered advisable to make no subdivisions of the 

 Weber Grits formation, and the whole is therefore included under one color 

 {g). On the more detailed maps, however, a subdivision of the Weber Grits, 

 designated the Weber Shales, has been distinguished by a distinct color (/). 

 The beds included under this name are extremely variable in lithological 

 character and in thickness. They constitute a transition series between the 

 massive limestones below and the characteristic coarse sandstones of the 

 Weber Grits above. They consist of argillaceous and calcareous shales 

 alternating with quartzitic sandstones. The former are generally carbona- 

 ceous, and in their extreme type pass into an impure anthracite. The cal- 

 careous shales, on the other hand, are locally developed into a considerable 

 thickness of impure limestone, which is very rich in fossil remains. Owing 

 to its variable character and to the fact that the dividing plane between 

 this and the preceding is frequently occupied by beds of porphyry, it is 

 difficult to assign a definite thickness to the formation. It may, however, 

 be assumed as varying from 150 to 300 feet. 



In Leadville itself a thin bed of quartzite is often found immediatelv 

 above the Blue Limestone, and on Iron hill is a greenish argillaceous shale,, 

 called the Lingida shale, from the abundant casts of this fossil which it 

 contains. The coal development attains a thickness in one case of seven 

 feet, but is extremely impure and gives little promise of any economical 

 value. 



Fossils. — The most common form is Lingula mytiloides, Meek, which is 

 supposed to correspond to L. ovalis, Sowerby. Besides these were obtained 

 from several diflferent localities the folio winer : 



PhiUipsia, sp.f (P. major?) 



Profhicttis cora. 



Prodnctus semiretienlatua. 



Produetns pcrtenuis. 



Productus murlcatus. 



Productus Nebrascensis. 



Spirifera cameratus. 



A viculopecten rectUaterarins. 



Ortliis carboiiarinfi. 



IStreptorhj/ncltus cra,ist(ii (crenistria). 



Chonetes granuli/era. 



Discina nitida. 

 MacrochcUus ven (ricosus. 

 Archaoccidaris. 

 Eoccidaris Halliana. 

 Fenestella ])erelegans. 

 Rhomhopora lepidodendroides. 

 Myal'nia perattenuata. 

 Polyphemopsis, (like P. chrysalis). 

 Pinna, sp.? 

 Polypora, sp. uudet. 

 Palaschara, sp. uuilet. 



