NO. 30 



SMITHSONIAN EXPLORATIONS, I < ) I _' 



Geological Survey and the Q. S. National Museum, was to obtain 

 material for volumes on the Cambrian and ( )rdovician strata of 

 Maryland, to form a part of the series of memoirs published by that 

 State. 



This work was done in such detail that it was possible to map the 

 Hagerstown and Williamsport quadrangles of western Maryland, 

 embracing all of the Appalachian Valley in that State. The various 

 formations making up the great Shenandoah limestone series were 









"X 







Fig. 56. — Fossil alga, Cryptosoon, exposed along the railroad near Antietam 

 Station, Md. Photograph by Bassler. 



first studied, with the result that eight distinct formations, aggre- 

 gating 10,000 feet in thickness, were recognized and mapped. Dur- 

 ing the process of the mapping, large collections of both rocks and 

 fossils, illustrating all the formations of the Shenandoah limestone, 

 were obtained. 



In addition, numerous photographs were taken, showing some of 

 the more interesting features of the geology. Two of these are here 

 reproduced. Figure 56 illustrates a reef of the hydrocoralline or 

 calcareous alga, Cryptozoon, as shown on Antietam Battlefield. This 

 reef may be noted wherever the base of the Upper Cambrian (Cono- 



