G6 THE CAMBRIAN AND ORDOVICIAN DEPOSITS or MARYLAND 



Waynesboro formation is nothing but a surface remnant, all the valley 

 east of the line first mentioned is composed of the Tomstown limestone. 



THICKNESS. In spite of numerous good exposures, no continuous sec- 

 tions of any thickness of the Tomstown limestone are exposed in Mary- 

 land, and indeed no place has been found where the normal sequence can 

 be determined. In southern Pennsylvania an approximate thickness of 

 1000 feet has been measured. This has been accepted as the thickness in 

 Maryland, although in the southern half of the state where the marbles 

 are well developed a greater thickness is possible. 



AGE AND CORRELATION. No fossils have so far been noted in the 

 Tomstown limestone in Maryland and indeed the sheared marbles and 

 dolomitic strata of the formation are not favorable for the occurrence of 

 organic remains. In southern Pennsylvania near Roadside and near 

 Waynesboro, fragments of the mollusk shell Salterella have been collected. 

 A few miles north of this at the foot of the mountain east of Little 

 Antietam Creek fragments of the characteristic Lower Cambrian trilobite 

 Olenellus were discovered by Walcott. A Lower Cambrian age for the 

 formation is therefore accepted, although the paleontological evidence is 

 still quite meager. Fossil evidence in the rocks holding the same strati- 

 graphic position in states to the south is also very slight, but favors the 

 same age. The most interesting of these fossils is a large species of 

 Archeocyathus recently found in the Sherwood limestone and a similar 

 large species of the same genus in the Shady limestone. 



In contrast with the few fossils of the areas just mentioned is the 

 abundant, well-preserved Lower Cambrian fauna found in limestones 

 and shales in the vicinity of York and Fruitville, Pennsylvania. It seems 

 probable that these f ossilif erous strata form a part of the Tomstown 

 limestone, but the lithology is so different that a close study of the inter- 

 vening area is necessary before this correlation can be made with 

 certainty. 



THE WAYNESBORO FORMATION 



Viewed as a lithologic unit the most obvious and easily recognized 

 formation in the Shenandoah limestone series is the mass of reddish to 

 purple calcareous sandstone and shale here known as the Waynesboro 



