MARYLAND GEOLOGICAL SURVEY 113 



some difficulty, and the present author was fortunate in having this earlier 

 work upon the subject even though he is unable to agree with some of the 

 conclusions. Comparison of the four structure sections across the 

 Frederick Valley, here presented as fig. 12 with that published by Keyes, 

 will show that the present conception of the structure and stratigraphy 

 differs radically. 



The lowest sedimentary rocks of this particular region are comprised in 

 the Lower Cambrian quartzites, the Weverton sandstone and the succeed- 

 ing Lower Cambrian Harpers shale exposed in Catoctin Mountain. Sugar 

 Loaf Mountain, on the east, likewise is composed of Lower Cambrian 

 quartzite. In the opinion of the writer the limestone series does not pass 

 upward on the eastern side of the valley into Hudson River shales, but it 

 is faulted against shales and schists which are of pre-Cambrian age. 

 Along the western side of the Frederick Valley the limestones are covered 

 by the conglomerate, red sandstone and shale of the Newark series except 

 in two areas where stream erosion has cut deeply into and in places almost 

 to the base of the underlying limestones. 



The structural relations of the Frederick Valley are so complicated that 

 it would be difficult to unravel the stratigraphy were it not for the occa- 

 sional presence of fossils. Determinable, though but rarely preserved, 

 fossil remains have been noted at numerous places in the valley in two 

 distinct kinds of rocks, namely, in dark blue thin-bedded strata, known 

 locally as the building rock, and in massive, rather pure, blue to white 

 limestone that is quarried for lime. The fossils in the quarry rock have 

 been found distributed through several hundred feet of strata. They 

 consist mainly of cephalopod shells which are closely related to lower 

 Beekmantown species. The fauna found in the building rock consists 

 of a brachiopod and a trilobite of types which are unquestionably of post 

 Beekmantown age. By fossil evidence, therefore, the age of the quarry 

 rock is established as older than the building rock. This conclusion is 

 borne out also by the structural relations of the beds, the building rock 

 being invariably infolded in the quarry rock. In all probability, the line 

 of contact between the limestone which forms the floor of the valley and 



