Maryland Geological Survey 141 



Vertical Total 

 thickness vertical 

 feet thickness 



Shaly limestone 3.4 77.3 



Stromatopora reef. Upper part shaly 3.3 73.9 



Shaly limestone 0.8 70.6 



Massive granular limestone 4.5 69.8 



Argillaceous limestone, thin and medium-bedded. Some stro- 



matoporoids 13.6 65.3 



Massive reef consisting wholly of stromatoporoids 6.5 51.7 



Shaly limestone partially concealed abounding in Spirifer 

 vanuxemi var. prognosticus. Tentaculites gyr acanthus, crin- 



oids, delicate, branching Bryozoa 20.2 45.2 



Dark blue nodular limestone abounding in Favosites helder- 



bergicB prwcedens 3.0 25.0 



Largely concealed along track. At bottom of unit a coral reef 

 abounding in Favosites helderbergiw prwcedens and contain- 

 ing Hahjsites catenulatus 22.0 22.0 



Concealed. 



Thickness of Helderberg exposed 158.7 



V. Section at Pinto 

 One of the best exposures of Middle and Upper Silurian rocks in the 

 State occurs at Pinto, Maryland. The section extends from the base of 

 the Clinton to the middle of the Keyser. The Tonoloway is typically ex- 

 posed and the contact between it and the Keyser can be well observed. 

 The lowest beds of the Keyser are exposed on the north side of the Balti- 

 more and Ohio Railroad just east of Potomac Station. The remainder of 

 the Keyser is partly concealed, but by going up the hill much of it can be 

 seen. The top of the " Salina " was placed by Rowe and Schuchert ' at 

 the uppermost exposure of limestone in the railroad cut. While the lime- 

 stones exposed in the cliff east of the station are not very fossiliferous, 

 Camarotcechia litchfieldensis and Siroplieodonta bipartita, two New York 

 Cobleskill forms, are found here together with Spirifer modestris, a 

 characteristic Keyser species. A heavy crinoid bed is present while Clado- 

 pora rectilineata occurs in the greatest abundance below it. The Gypidula 

 coeymanensis var. prognostica zone occurs to the west. The upper portion 

 of the section is cut out by a fault, but the Xew Scotland beds can be seen 

 upon the hillside to the northeast. 



1 Rowe manuscript. Library Johns Hopkins University. Schuchert. Proc. 

 U. R. Nat. Mus., vol. xxvi, 1903, p. 423. 



