52 CD. Walcott— Cambrian Rocks of 



The slabs were submitted to Mr. C. D. Walcott, who has 

 kindlv made the following statement regarding them : " I have 

 studied the specimens of slate showing crinoidal remains and 

 come to the conclusion that they belong to the Trenton-Lor- 

 raine or upper portion of the Ordovician fauna. One of the 

 larger columns is closel} T allied to Schizocrinus nodosus, and 

 some of the heads, although indistinct, approach closel} 7 to 

 Heterocrinus and Poterocrinus. If these suggestions are cor- 

 rect, the slates are to be correlated with the Lorraine or Hud- 

 son series and in the same horizon with the Peach Bottom 

 slates of Pennsylvania. 



The occurrence of fossiliferous beds in the crystalline area 

 of Virginia will greatly aid in the determination of the age 

 and structure of its rocks, and the discovery at Arvon may be 

 regarded as a most fortunate one. There are several other 

 belts of slate in the Piedmont region, notably in Virginia, 

 Maryland and Pennsylvania, and it seems probable that other 

 similar localities may be discovered. I have recently explored 

 one of these belts which comprises the easternmost rock outcrop 

 along the edge of the coastal plain from north of Fredericks- 

 burg to a short way beyond the Occoquan River, but without 

 finding fossils. This belt will be designated the " Quantico 

 slates" on the "Fredericksburg" and " Mount Vernon " sheets 

 of the U. S. Geological Survey. Its slates are similar to those 

 of Arvon, but somewhat more altered, and they were at one 

 time worked to some extent for roofing slate, although most 

 of the beds contain more or less pyrite which renders them 

 unserviceable for roofing. 



Aet. VI. — Notes on the Cambrian Rocks of Virginia and 

 the Southern Appalachians • by Chas. D. "Walcott. 



In connection with the study of the Cambrian rocks and 

 faunas of North America I made a hurried reconnaissance in 

 the fall of 1891 of the sandstone series of central Virginia. 

 In company with Mr. Bailey Willis and Prof. H. D. Campbell 

 an examination was made of the Balcony Falls section along 

 the line of the James Piver. It failed to bring to light any 

 traces of organic remains other than the Scolithus that occurs 

 in the massive quartzite below the ferriferous shale at the 

 western end of the gorge. On the following day well pre- 

 served specimens of a species of Ptychoparia were discovered 

 in the shale, by the roadside, about a mile south of Natural 



