Stevenson.] iOU [Nov. 21, 



interesting memoir on the gypsum deposits of Castellina Marittima tells of 

 conditions very similar. The amygdiiles of gypsum are of large size, and are 

 associated with marly gray to yellow clays. He ascribes the formation of 

 this gypsum to the action of sulphur springs on calcium carbonate held in 

 solution ; so that the carbonate was changed into sulphate and deposited as 

 such in the littoral lakes of the Middle Miocene. Dr. Newberry, on the 

 authority of Dr. J. M. Locke, has informed the writer that something very 

 like this is going on in Lake Utah, where the calcareous wash from the 

 Wasatch mountains at the east meets the pyritous wash from the Oquiah 

 range at the west, so that calcium sulphate is depositing in the lake. 



The origin of the Holston gypsum is to be accounted for in some similar 

 way. Several deep basins were occupied by lakes ; that of the Saltville 

 basin received not a little calcareous matter from the Lower Carboniferous 

 beds forming its northerly shore, and some doubtless was received from 

 the wash of the Knox beds on the southerly shore ; in the basins further 

 east the calcareous matter derived from the wash should be far inferior to 

 the argillaceous matter. But the composition of the gypsum shows less of 

 the red clay at Buchanan's than at Saltville. The principal source of the 

 calcareous matter must be looked for not in the wash from the shores, but 

 in springs. That calcareous springs can produce deposits as extensive as 

 those of this region is sufficiently shown by the extensive deposits around 

 many of the springs at the far West. The calcium carbonate in solution 

 would be converted into calcium sulphate by the sulphurous springs also 

 issuing from the fault, and the gypsum would be deposited as such. 



The red marly clays were derived from the wash, and are more abund- 

 ant at Saltville, where the soft red shales at the top of the Lower Carbo- 

 niferous are fully exposed on the northerly side of the basin. Undoubtedly 

 not a little of the gypsum is derived from this wash, but, comparatiyely 

 speaking, the quantity must have been insignificant. Had the basins been 

 very large, such as that of the ancient Lake Lahontan, so well described by 

 Mr. L C. Russell,* the detrital material would have been dropped at the 

 shore, and the calcareous matter would have been deposited by itself in 

 the middle of the lake ; but the Holston basins are very small ; the region 

 is one which always had a great rainfall, so that the wash of sand and clay 

 would be very considerable. The amount of foreign matter and its distri- 

 bution in the gypsum are conclusive. The sodium chloride must have 

 come from springs and it may have been derived from the great sand- 

 stones under the valleys. Whatever was the source, the supply appears 

 to have been cut off at about the same time throughout the whole region, 

 for the top of the " saltrock " is reached at 215 feet at Saltville and at 300 

 feet in the Taylor shaft or at approximately the same absolute level. 



Cafici, in his observations of the Sicilian gypsiferous deposits, and Ca- 

 pellini, in his studies of the Tuscan deposits, find evidence of alternating 

 periods of activity and quiet in the springs ; for the fossiliferous shales 



* Russell. Sketch of the Geol. Hist, of Lake Lahontan. Third Annual Report 

 U. S. Geol. Surv., 1881, 1882. 



