26 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 70 



sedimentary rocks of the region were massive, unfossiliferous lime- 

 stone probably of Pre-Cambrian age, with a great erosional uncon- 

 formity at their top. Immediately following this unconformity is 

 an arenaceous limestone several feet thick containing the Corynex- 

 ochns fauna hitherto believed to be of Middle Cambrian age. Fol- 

 lowing this bed, in apparently normal succession, are the well-known 

 Lower Cambrian shales containing Olcncllus and other trilobites. 

 In figure 25 the point of contact between the two Lower Cambrian 

 formations is indicated at C. Collections of two faunas of Lower 

 Cambrian age were secured during these studies. 



Fig. 26. — Open iron ore pit at Cornwall, Pa. Photograph by Resser. 



Dr. Resser also spent some days in collecting mineral specimens 

 from the celebrated ore banks at Cornwall, Pennsylvania, a locality 

 famous for its well-preserved minerals, but unfortunately poorly 

 represented in the Museum collections. These ore banks are in the 

 hills between Lancaster and Lebanon counties and, as they have been 

 worked since 1853, they are now great open pits from which the 

 minerals can be obtained. The ore is the iron oxide magnetite, 

 formed along the lines of contact of an igneous mass intruded into 

 Paleozoic limestone. The magnetite often occurs well crystallized, 

 but the mineralogical interest of the locality lies in the minerals of 

 copper, iron, and magnesium silicates which were formed with the 

 magnetite. The i)hotograph (fig. 26) shows the arrangement of 



