426 CHARLES S. PROSSER 



(Clarion) coal with a thickness of two feet which was reported 

 by the miners to reach 4^ feet. At Westernport nearly 100 

 feet above the base is an impure coal, called the " Split six-foot " 

 by the miners, showing a thickness of 4 feet, and 130 feet above 

 the base is the most valuable coal seam of this formation, the 

 "Davis" (Lower Kittanning), commonly known as the "Six- 

 foot," with a thickness of about 5 feet in the lower George's 

 Creek valley. Nearly 170 feet above the Davis seam is the 

 "Thomas" (Upper Freeport) coal, which forms the top of the 

 formation, and from its general thickness in the George's Creek 

 valley is known as the "Three-foot" seam. Fossil shells have 

 been found in the black or bluish shales at a few localities. The 

 thickness of the formation is about 300 feet. It is named from 

 the exposures on the Allegheny River in western Pennsylvania, 

 is very generally called the Lower Productive-measures, is No. 

 XIII of the Pennsylvania survey and includes the Savage forma- 

 tion and lower part of the Bayard of the Piedmont folio. 



Conemmigli formation. — The area south of the Pennsylvania 

 line to a parallel line passing through Little Alleghany and to 

 the west of the foot of the western slope of Little Alleghan}^ 

 and Piney mountains is largely covered by this formation. Then 

 it extends parallel to Dan's Mountain, to the southwestern part 

 of the county and covers a large portion of the steep slopes of 

 the hills bordering the lower George's Creek valley, continuing 

 up the valley to Ocean. It also appears in the upper part of a 

 number of the small valleys along the western border of the 

 county. The lower part of the formation, representing the 

 Mahoning sandstone, is frequently a massive gray sandstone with 

 bands of yellowish shales reaching a thickness of about 100 

 feet. In the upper part of this sandstone, about eighty-five feet 

 above the Thomas coal, is a coal seam about two feet in thick- 

 ness underlain by a stratum of fire clay. The succeeding rocks 

 are grayish to brownish sandstones and yellowish to gray and 

 black arenaceous and arigillaceous shales with beds of coal and 

 fire clay. In some of the localities there are quite massive gray 

 to brownish-gray sandstones near the middle and top of the 



