88 THE CAMBRIAN AND ORDOVICIAN DEPOSITS or MARYLAND 



mass. No such distinction as this can be drawn in nature because there 

 are all gradations of arrangement. 



The observations of Ulrich, Stose, Butts and other geologists who have 

 had numerous opportunities to study the edgewise beds, all tend to the 

 conclusion that these conglomerates are not organic; but are composed of 

 fragments formed on tidal flats by mud cracks. The Appalachian early 

 Paleozoic formations are practically all shallow-water deposits in which 

 the area was often subject to uplift above the sea level. Mud flats which 

 by uplift are exposed to evaporation soon develop the usual shrinkage 

 figures known as sun cracks and the edges of these to-day curl up and are 

 broken off and tossed about by the wind. This same condition has 

 occurred time and again in the past, and indeed limestones still preserving 

 well-defined sun cracks with the edges curled up and ready to be formed 

 into edgewise conglomerates have been observed. 



FOSSILS OF CAMBRIAN AGE 



In spite of the considerable thickness of Cambrian rocks developed in 

 the Appalachian region of Maryland, and the careful search that has been 

 made, fossils of this age are exceedingly rare. Usually no trace of 

 organisms can be detected in the rocks, and the few specimens noted have 

 always been fragmentary and poorly preserved. These few remains occur 

 in the Harpers schist, Antietam sandstone, and Tomstown limestone of 

 Lower Cambrian age, in the two Middle Cambrian formations, the 

 Waynesboro formation and Elbrook limestone and in the Upper Cambrian 

 (Ozarkian), Conococheague limestone. The basal Cambrian Loudon 

 formation and the succeeding Weverton quartzite are lithologically of 

 such a nature that fossils would not be expected in them, but the over- 

 lying formations are more promising in this respect and may possibly 

 yield to some fortunate collector more respresentative faunas than known 

 at present. Fairly well-developed Lower and Middle Cambrian faunas 

 are known in the Appalachians both north and south of Maryland, but it 

 appears that the strata bearing them are usually not represented in the 

 Maryland section. For example, the Lower Cambrian strata at York, 



