1897.] : Petrography. 523 
One of the basic concretions in the Picota area has the composition of 
teschenite. Its analysis gave : 
SiO, TiO, AlO% Fe.0; FeO MgO CaO NaO KO CO, PO; H:O Total 
49.67 4.14 14.56 6.09 6.41 4.66 14.87 4.25 1.94 .40 .52 1,18 = 100.82 
Another is an essexite with the composition : 
SiO, TiO, AlO, FeO, FeO MgO CaO Na,O K,O H,O Total 
Vianan yaaani 
49.67 not det. 17.99 13.06 3.06 6.63 6.21 2.62 .86 =— 100.10 
The contact products formed in the surrounding slates, graywackes and 
quartzites are hornstones, knotty schists and other contact schists like 
those so frequently found around bosses of granite. Diabase horn- 
stones (cordierite-bearing and cordierite-free) are contact facies of 
igneous rocks in the vicinity of the syenite intrusion. 
Notes.—Jaggar’ has constructed a simple instrument to use on the 
microscope stage for inclining a thin section in such a manner that 
optical axial angles may be observed in sections cut at random. 
Merrill® continues his contributions to the study of rock weathering 
in a paper on the weathering of micaceous gneisses in Albemarle Co., 
Virginia. The results communicated confirm those obtained in pre- 
vious investigations. The red color of the residual soil in this case, as 
well asin the south generally, is thought to be purely a superficial 
phenomenon. It is accounted for by the accumulation of the coloring 
matter distributed through the rock in the residue left by the weather- 
ing processes. Brilliant colors in residual soils are thus regarded as 
evidences of long continued weathering action. The author would 
limit the use of the term ‘weathering’ to the alteration “ processes 
going on within the zone of oxidation and resulting as a rule in the 
destruction of a rock mass as a geological body.” The deeper seated 
changes resulting in the alteration of the rock constituents without 
changing the character of the rock as a whole, he would term hydro- 
metamorphism. ; 
7 Amer. Jour. Sci., IJI, 1897, p. 129. 
8 Bull. Geol. Soc. Amer., Vol. 8, p. 157. 
