552 THE JOURNAL OF GEOLOGY. 



tortrix septemdentata Gabb, Mesalia claibornensis Con., Turritella 

 nasuta Gb., Natica limida Con., Sigaretus declivis Con., S. incon- 

 stans Aid., Belo sepia ungula Gb. 



Yegua Clays. — This sub-division was proposed to include the 

 gypseous and saliferous clays, lignites and sands lying between 

 the Marine beds and the sandstones of the Fayette with which 

 they were united in the first use of that name. The area occu- 

 pied by them is, for the most part, only gently rolling, except 

 toward the southwest, where it sometimes happens that consid- 

 erable hills occur, the summits being capped by the harder 

 sandstone or quartzite of the Fayette beds. 



The clays are dark blue, weathering to a dirty yellow, with a 

 profusion of crystals of gypsum. In places the clays are mas- 

 sive, at others laminated. The sands are gray and white, often 

 laminated or cross-bedded, but sometimes massive. The fossil 

 wood contained in them is simply silicified and not opalized, as 

 in the succeeding beds. The brown coal and lignite deposits of 

 this sub-division are as extensive as those of the Lignitic stage, 

 beds with a measured thickness of sixteen feet having been 

 observed on the Colorado. 



While the lithological characters of the Yegua clays are 

 clearly marked and plainly traceable entirely across the state, its 

 fauna connects it directly with the Marine beds. Typical expos- 

 ures of the beds may be seen near Alto and Lufkin, on the 

 Yeguas in Lee county, and between Pleasanton and Campbellton. 



In addition to the many forms common to this and the Marine 

 beds, the following seem to belong exclusively to the Yegua : 



Tellina mooreana Gabb var., Turritella 7iasuta var. houstonia 

 Har., Natica recurva Aid. 



Fayette sands. — This name was originally applied by Penrose 

 to the entire series of deposits between the top of the Marine 

 beds and the base of the Coast clays. It is used here, with a 

 greatly restricted significance, for that sub-division of the Ter- 

 tiary to which the name is most applicable. This is a series of 

 sands and sandstones with some clays, which contain a large 

 amount of opaline and chalcedonic materials. The sands are 



