MARYLAND GEOLOGICAL SURVEY 83 



Cambrian and Middle Ozarkian formations. Moreover, its affinities lie 

 nea-rer the Ozarkian species than the Cambrian, so that its evidence, so far 

 as it goes, favors assignment of the Conococheague to the Lower Ozarkian. 

 Vhe brachiopod, also, as now understood, has too wide a range for detailed 

 stratigraphic work. The two species of Cryptozoon at the base occupy this 

 position throughout a large part of the Appalachian Valley and serve as 

 excellent guide fossils. 



The Maryland early Paleozoic section is far from complete and the 

 age of the Conococheague limestone must be determined from more fully 

 developed sections in other areas. The Cryptozoon fauna occurs in central 

 Pennsylvania in the Gatesburg dolomite which, roughly speaking, is the 

 equivalent of the Conococheague limestone. Beneath the Gatesburg dolo- 

 mite, and separating it from the Middle Cambrian, Elbrook, is an Upper 

 Cambrian formation, the Warrior limestone. To the south in Virginia, 

 Tennessee, and Alabama, the same Cryptozoon fauna is also known and in 

 each case it is separated from the Middle Cambrian equivalents of the 

 Elbrook limestone by Upper Cambrian formations of great thickness and 

 containing well-developed faunas. Evidently then we must conclude that 

 the contact between the Elbrook and Conococheague in Maryland is 

 unconformable and represents a stratigraphic break of considerable 

 magnitude. 



Cryptozoon Reefs. 



The basal 15 or 20 feet of the Conococheague limestone usually exhibit 

 layers so uniformly and curiously laminated over considerable areas that 

 this phenomenon cannot be attributed to ordinary plications in the strata. 

 All of the sandy laminated and banded portions of the formation show a 

 wavy or crinkled structure, especially where strong folding has occurred, 

 but the laminations of the basal beds are of a quite different nature. The 

 limestones in which the latter laminated structures occur are not of the 

 usual banded type, but are composed of a massive, rather homogeneous 

 and somewhat purer rock. In an edge view of a stratum the rock is seen 

 to be made up of thin, parallel films of material piled one upon the other. 



