Wm. F. Prouty — Meso-Silurian Deposits of Maryland. 569 



main facts supporting this conclusion are : the top Clinton 

 sandstone increases gradually in thickness from seven feet at 

 Pinto to some sixty-five or seventy feet in the eastern exposures ; 

 the bottom Rochester shales increase in thickness and the 

 bottom limestones consequently decrease in thickness in passing 

 from west to east ; the top Rochester sandstone, like the top 

 Clinton sandstone, thickens from eight feet at Pinto to some 

 fifty feet or more in the eastern exposures. If we assume then 



Fig. 2. 



4 5 



West 



6 7 



S.S. 



s.s. 



East 



Lower 

 'Ore" 



1. Pinto Section. 



2. Cedar Cliff " 



3. Eose Hill " 



Cumberland Section. 

 Six-mile-house ' ' 

 Flintstone " 



Great Cacapon Section. 

 Keefers Mt. 



that the Maryland Meso-Silurian deposits were laid down in a 

 narrow basin of deposition, then Pinto must be east of the 

 central axis of the basin or else the western shore line of this 

 narrow sea must have been much lower than the eastern land 

 was. It is not improbable that both these conditions were true. 



Fossil Zones. 



In Clinton. — 



The Clinton formation, so far as studied, has not shown any 

 well-marked continuous fossil zones. Portions of the strata 

 are much more fossiliferous, however, than others, and the 

 formation as a whole is naturally divisible into four parts : 



Am. Jour. Sci.— Fourth Series, Vol. XXVI, No. 156.— December, 1908. 

 40 



