WALcorr.l MARYLAND AND VIRGINIA. 133 



MARYLAND. 



A brief description is given by Prof. P. T. Tyson, in his first report, 1 

 of the rocks in Maryland referred to the Primal series of Rogers. Two 

 formations are referred to the Primal : (1) a hard sandstone; and (2) a 

 slate, varying in color from gray to brownish and greenish. On the 

 map accompanying the report the geographic distribution of the Primal 

 series is indicated. 



VIRGINIA. 



One of the earliest attempts to differentiate, by lithologic characters, 

 the formations of the Blue Eidge of Virginia is on the map of a section 

 crossing it east of Winchester. 2 The Transition, or blue limestone, is 

 represented as passing beneath the limestone shale that, in turn, dips 

 beneath a gray schistose rock. This section is of interest only when 

 interpreted by the later sections of Prof. Rogers. 



Prof. William B. Rogers describes in the Second Report of the Prog- 

 ress of the Geological Survey of Virginia the Primal series in the 

 central counties of the State, or of the Great Valley, as follows : 



(No. 1.) This rock or group of rocks, which is frequently exhibited in extensive 

 exposures along the western side and base of the Blue Ridge, more especially in the 

 middle counties of the valley, is usually a compact, rather fine-grained, white or 

 yellowish gray saudstone. Where resting on the declivity of the ridge it presents a 

 gentle inclination to the northwest — while thejsubjacent and more ancient strata of 

 the ridge, in almost every instance, dip steeply to the southeast. In Page, Rocking- 

 ham, Augusta, and Rockbridge counties this rock forms the irregular and broken 

 ranges of hills lying immediately at the foot of the main Blue Ridge, and sometimes 

 attaining an altitude little inferior to that of the principal mountain. A level region, 

 sometimes of considerable breadth, and strewed profusely with the fragments of this 

 rock, in general intervenes between these rugged hills and the first exposures of the 

 valley limestone. * * * Talcose and micaceous matter make their appearance in 

 it. * * * This micaceous and talcose variety is sometimes found in the same hill 

 underlying the more purely silicious rock. The latter, in nearly all the exposures 

 from the Balcony Falls to Thornton's Gap, as well as in various other places, exhibits 

 vague, fucoidal and zoophytic impressions on the surfaces of bedding, together with 

 innumerable markings at right angles to the stratification, penetrating in straight 

 lines to great depths in the rock, and from their frequency and parallelism deter- 

 mining its cleavage in nearly vertical planes. These markings are of a flattened, 

 'cylindrical form, from one-eighth to one-tenth of an inch broad, giving the surface of 

 the fractured rock a ribbed appearance, and resembling perforations made in sand 

 which have been subsequently filled up without destroying tne distinctness of the 

 original impression. Precisely similar markings are found in great abundance in the 

 white compact sandstone occurring at a higher point in the series, associated with 

 numerous unequivocal impressions of fucoides. 



The extent to which these sandstones are developed is comparatively inconsidera- 

 ble in the southern and northern counties of the valley, and their structure and com- 

 position are in many respects materially changed. 3 



1 First Report of the State Agricultural Chemist of Maryland. Annapolis, 1860, pp. 34, 35. 



2 Clemson, Thos. G.: Notice of a geological examination of the country between Fredericksburgh and 

 Winchester, in Virginia, including the gold region. Geol. Soc. Penn., Trans., vol. 1, 1835, map, oppo. 

 p. 298. 



3 Second report of the progress of the geological survey of the State of Virginia, for the year 1837. 

 Richmond, 1838, p. 14. 



