H. D. Campbell — Cambro-Ordovician Limestones. 447 



Liberty Hall limestone. — In describing a section through 

 this region in 1879, J. L. Campbell* used the name Lexington 

 limestone for this formation, but inasmuch as the same name 

 is given to certain Silurian rocks in Kentucky, f it has been 

 rechristened Liberty Hall limestone from the name of an old 

 historic ruin which is constructed on and of this rock, and 

 which has been standing for more than a century and is as 

 well known in this region as Lexington itself. 



The Liberty Hall limestone is usually a succession of rather 

 evenly banded beds of fine-grained, dark blue limestone and 

 darker, more argillaceous limestone which weathers shaly. As 

 we ascend into the formation calcareous shale predominates 

 and limestone beds are less frequent. In this region the forma- 

 tion has been much fractured and folded, and sometimes 

 appears massive with innumerable veins of infiltration of cal- 

 cite filling the crevices. Again it appears shaly after long 

 exposure to weather.' Brachiopods and trilobites of Mohawkian 

 age are especially abundant in the lower beds. From the top 

 of the Murat through the limestone and calcareous shale, so 

 long a*s it carries conspicuous limestone beds, the Liberty Hall 

 limestone is about 1000 feet thick. Then follows about 600 

 feet of shale and slabby sandstone to the bottom of the first 

 bed of quartzite above the Valley limestones. The thick beds 

 of shale above the limestones, both northeast and southwest of 

 the section here considered, give rise to another problem of 

 correlation. 



Washington and Lee University, 

 Lexington, Virginia, October 31, 1905. 



*This Journal, xviii, 1879, p. 29. 



fU. S. Geol. Surv. Geol. Atlas of U. S., Folio No. 46, 1898. 



