1908 ] 
Flint-like Slate Near Chapel Hill 
5 
considered the formation of the hornstones and flinty slates as 
due to a change in the latter rocks. The existence of tuff deposits 
along this part of Morgan’s Creek mentioned by Williams and 
quoted by Nitze is strongly discredited by Professor Collier Cobb, 
who has had Occasion to learn thoroughly the structure of the 
region in question during the course of his work at Chapel Hill. 
Professor Cobb, however, takes his classes to such tuff deposits 
’ southwest of the village, and it is these that Williams and Nitze 
i have evidently confused with the slates of Morgan’s Creek two 
j miles south of Chapel Hill. 
As Professor Cobb has pointed out to the writer, these slates are 
I bedded alternately with sandstones and conglomerates. The con- 
glomerates are composed of well-rounded pebbles of several kinds of 
volcanic rocks, but are by no means volcanic agglomerates. The 
j slates are coincident in dip with the sandstones and conglomerates 
with which they are associated, and, from all field evidence obtain- 
able, seem to have been deposited as regular members of the sedi- 
jj mentary series. 
Specimens of the rock for investigation were obtained near the 
I dam at Purefoy’s Mill. The general macroscopic description 
given by Nitze applies very well to the rock from this locality. 
In handspecimen , the rock is olive green in color, weathering to 
brownish clay; banding faint, becoming more apparent on a 
weathered surface; appearance waxy; structure dense and com- 
| pact, with occasional minute reflecting crystal surfaces; trans- 
lucent on edges; fracture conchoidal; very brittle; hardness 6.5. 
Its resistance to abrasion is evidenced by the fact that all of the 
I j arrow heads and spear heads of primitive man found in the 
vicinity of Chapel Hill are made of this material. 
Microscopically, this slate is seen to be a true crypto -crystalline 
i rock, containing the minerals feldspar, quartz, kaolin, and epi- 
dote. The groundmass is composed of very fine quartz crystals 
and minute feldspar fragments through which kaolin scales are 
plentifully scattered. Larger crystals of feldspar form a promi- 
nent feature, and occur individually or in groups throughout the 
Igroundmass. Sections cut at right angles to the lamination show 
i ; that the kaolin scales occur in distinct bands varying in width 
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