PALEOZOIC GROUP. 299 



often itself resting directly upon Fotsdam limestone or sandstone, there is a 

 well marked aggregate of very fine-grained compact limestones, or white or 

 grey dolomites. To some of the strata the name "Burnet Marble" has 

 been applied by the earlier geologists, from the great development of the 

 series near the town of Burnet, and in the neighboring portions of Burnet 

 County. In Hoover Valley, along the Silurian escarpment at the sources of 

 Webster Creek and Peters Creek, the beds are well exposed, and much 

 hope has been entertained by the citizens that the most uniform beds may 

 possess commercial value as a "lithographic stone." The results of tests are 

 given in another chapter. The structural feature of most interest is the ap- 

 parent unconformity between the base of this Division and the summit of the 

 Wyo Division. This is not necessarily in the nature of a catastrophic break, 

 but more probably of gradual subsidence; for the contact in the James River 

 valley and elsewhere is made through beds of passage partaking of the char- 

 acters of both sets. Some of the strata which are here regarded as basal 

 members of the Hoover Division are in composition mere transitionary relics 

 of the Wyo type. These, however, usually appear more like the Wyo beds 

 at a distance than upon close inspection. Even the uppermost wave-marked 

 layers have the texture of the limestone in part, thus standing below the 

 assumed base of the Series, with a mixture of Wyo and Hoover characters. 

 In places where the later shore line has been pushed inward beyond the 

 edge of the earlier coast, so as to bring the lower contact into junction with 

 the Potsdam limestone, the basal members are often pure limestones. At 

 other contacts of this kind, perhaps more common, the connecting beds show 

 evidence of a semi-fragmental origin, with limestone components of both 

 Cambrian and Silurian types. These last can hardly be classed as conglom- 

 erates, but they simulate them on fractured surfaces, in a peculiar manner. 

 The appearance is what one might expect from deposition in moderately 

 deep water subject to ebb and flow of fine sediments. 



Some of the facts seem to imply a throbbing or slight uplift in portions 

 of the district, accompanied by subsidence in other places, at a time subsequent 

 to the deposition of the passage beds, and antecedent to the epoch of Burnet 

 marble sedimentation. Were it not, however, for certain northwest dikes, 

 breaks, and dip courses which are best explained in this way, it might not 

 have been thought necessary to seek any other cause than that of differences 

 in depth of the sea in different places at one time. Still this could not alone 

 account for all the facts observed. 



There is a very convenient horizon for the provisional separation of the 

 Wyo and Hoover strata, although future studies may not warrant the estab- 

 lishment of a stratigraphic serial line at this point. This is at the lowest 

 known fossil horizon above the Wyo crags. Fortunately for our purpose 



