22 ‘J. L. Campbell— Silurian Formation in Virginia. 
dark shales alternating with sandstones more or less conglom- 
erate. The shales, however, predominate. Next comes a b 
(b) of very hard sandstone—quartzite; the upper and lower 
layers of which are more brittle than the main mass lying 
between them. This is succeeded by a much thicker mass of _ 
brown, cst and = shales (c), With: thin beds of brittle 
sandsto his mass is Soon disintegrated at the 
— River pass on eee hs ides, where its thickness is et tiies 
with numerous ps of mica disseminated ioe cher Up 
to this point we find only very faint indications of fossil — 
remains of either plant or animal, A few scolithus borings ~ 
(in. b and d) are found, but they are rare, in comparison with 
” Such is Prcteste B Rae ers’s rs a of the 
given - this heavy bed - rock by the Seolithus line- 
s are so numerous that I recently counted at 
Baoas Falls tions 150 of ‘nals extéoutitive projecting on one 
quare ‘root of surface. This may yery properly be called the 
lithus bed” of this Primordial formation. The thinner 
beds at the top and bottom disintegrate rapidly. Between nie ) 
and the first limestone of the valley is a thick mass of ferrugi- 
nous shales generally much disintegrated and _— with the 
