According to the Kingston Folio of the U. S. Geological Sur- 

 vey Atlas, the immediate rock formation is the Knox Dolomite, or 

 Magnesium Limestone of the Lower Silurian. But Dr. Gattinger 

 avers that the Chattanooga Black Shale (Devonian) and the Fort 

 Payne Chert (Lower Carboniferous) both crop out here. The fern 

 probably occurs in the latter. * Immediately above is the Bangor 

 Limestone, which supports the fern at South Pittsburg. 



b. The Smith Pittsburg Station. The Hart's-tongue was discov- 

 ered growing in a deep sink-hole near South Pittsburg, by Major 

 Cheathem, in 1879. t South Pittsburg is a town on the Tennessee 

 river, about three miles north of the Alabama boundary. Some 

 two miles southwest of the town, two spurs of the Cumberland 

 mountains, extending southeast into the level plain of the river, 

 form a narrow valley or "cove," as they say in Tennessee. To 

 reach the sink-hole, follow the cove a half mile, or until half way up 

 the mountain. Sixty feet to the left of this narrow valley and about 

 sixty feet above, there is an irregular fissnre in the Mountain lime- 

 stone, sixty feet long by twenty to forty feet wide and ninety-two 

 feet deep. Upon examination, a good-sized spring is found to 

 issue from a cave not more than twenty yards farther up the hill. 

 This spring, tumbling perpendicularly into the hole, strikes a pro- 

 jecting ledge some forty feet below. The water splashing from 

 tth ledge has worn a deep depression in the opposite side, and it 

 is chiefly upon this slope that the fern grows. The area covered by 

 the ferns is not over 200 square feet, and contained (in 1898) about 

 1 10 mature plants. A few are variously distributed along the sides 

 and edges of the chasm, with Asplenium parvulum. The soil is a 

 sticky, light-colored clay, formed from the disintegrated shales of 

 the upper mountain. The ferns are found mostly about fifty feet 

 below the surface, and are so sheltered that some of them the 

 direct sunlight never reaches, and can possibly reach none of them 

 longer than two hours a day. There is little variation in tempera- 

 ture, naturally, and they are always dampened by the spray of the 

 falling water. After its first drop of forty feet, the water trickles in 

 small streamlets over the rock walls and fragments the remaining 

 fifty-two feet, to disappear in a narrow fissure at the bottom of the 



* Dr. Gattinger has kindly furnished me full particulars regarding this sta- 

 tion. I am under obligation also to Mr. David White, of the U. S. Geological 

 Survey, Washington, D. C., for information relating to the geology. 



fBull. Torr. Bot. Club, Q: 350. 1879. 



