

290 THE CAMBRIAN. IwnfctL 



feldspar and kaoliu. The siliceous cement seems to Lave completely filled up the 

 interstices between the grains so as to give a tirra compact structure to the rock. 

 Portions of this rock seem to have been subjected to such changes as to render it 

 doubtful whether it should not be considered a grauular quartz and be classed among 

 the metamorphic rocks. Vegetable life seems to have commenced at the period of 

 the formation of this rock, because itcoutaius fossilized stems of plants. 



(•2) A slate varying in color from gray to brownish and greenish. It is ranked as 

 an argillite. but portions of it assume a marked talcose appearance, especially in the * 

 Catoctin Mountain and in parts of Middletown Valley, where it has been much di 

 turbed and altered by proximity to intrusive rocks. These last consist of amphibo- 

 lies (trap), porphyries, amygdaloid, serpentine, and epidote. This last-named rock is] 

 extensively developed both in large masses and intercalated between the slates, and 

 has largely contributed to produce the highly fertile soils of Middletown Valley. 



Approximate measurements of the thickuess of these strata have been made in 

 New York and Pennsylvania, but I have not as yet been able to obtain reliable in- 

 formation upon this point in our State. 1 



From this descriptiou aud the geographic distribution of the Primal 

 series as iudicated on the accompanying map, it is evident that the 

 quartzite of South Mountain, Pennsylvania, extends nearly north and 

 south, across Maryland, and that the slates and associated eruptive 

 rocks which form the main mass of South Mountain are included by 

 Prof. Tyson in the Primal series. In the sections of these slates aud 

 accompanying rocks in Virginia they are recognized as pre-Cainbrian^ 

 and it is very probable that those of Maryland nnd north into South 

 Mountain of Pennsylvania are also of pre- Cambrian age. The pres- 

 ence of the upper Primal slate of Rogers between the quartzite and the 

 Auroral limestone is not noted by Prof. Tyson. The fossilized stems of 

 plants referred to are probably the Scolithus borings found so abun- 

 dantly in the saudrock of Pennsylvania and Virginia. If the lowe^ 

 portion of the limestone series of Pennsylvania is of Cambrian age it 

 is probable that the extension into Maryland is the same. 



VIRGINIA. 



Prof. William B. Rogers's description of the geographic distribution, 

 strati graphic position, and character of the strata that he referred to the 

 Primal series, has been proved to be in a large measure essentially cor- 

 rect by the observations of geologists who have more recently studied 

 the formations referred to the Cambrian group. He described forma- 

 tion No. 1 as consisting in the most part of a close-grained white or 

 light gray saudstone, in some places containing beds of a rather coarse 

 conglomerate of white siliceous pebbles. Near the bottom, in many 

 instances, a brownish slaty sandstone occurs, alternating with the for- 

 mer, whilst toward the top or approaching the next formation the sand- 

 stone passes into reddish and brownish aud olive-colored argillaceous 

 slates. As far as known to him in his earlier work the formation ia 

 Virginia was exclusively confined to the western slope of the Blue 

 Ridge and the narrow belt of rugged hills aud mountains extending 



1 Tyson, Phillip T. : First report of the State agricultural chemist of Maryland. Annapolis, 18fifc 

 pp. 34, 35. 



