122 The American Geologist. February, looi. 
of gneissoid granite on the Connecticut river east of Middletown. The 
phenomena and inclusions of the inclosing schists prove the granite 
to be intrusive, in spite of the marked and persistent foliation. It as- 
sumes frequently the character of an "augen"-gneiss. Basic segregations 
or schlieren of dark color and fine grain are a common 
feature, strengthening the proof of an igneous origin, as do 
the asociated dikes of pegmatyte and the contact zone of granulyte. 
The component minerals, from which the chemical composition may be 
approximately deduced, are chiefly quartz, various feldspars and biotite, 
the feldspars including most abundantly orthoclase, with an acid plagio- 
clase and subordinate microcline. The accessories include titanite and 
a very little apatite and magnetite. In the granulyte garnet is the chief 
or only accessory. w. o. c. 
The Origin of Nitrates in Cavern Earths. By William H. Hess. 
(Jour. Geol., 8, 129-134.) 
The nitrates are not derived from the excrement of bats, as pop- 
ularly supposed, but have their origin in the oxidation or nitrifi- 
cation of organic matter in the surface soil through the agency of 
bacteria, and the subsequent leaching of the nitrates so formed down- 
ward into caverns, where they slowly accumulate with other salts as 
the water escapes by evaporation. This explanation is in harmony with 
the fact that bats penetrate but short distances from the entrance to a 
cavern, while the distribution of the nitrates is entirely without refer- 
ence to the entrance, the cavern earh of the Mammoth cave having 
been worked for nitrates for a distance of over five miles from the 
only opening to the surface. Three analyses show that nitrates form 
but a small part of the soluble salts of the cavern earth, which include 
also sulphates a^d chlorides, and may aggregate as much as 13 per 
cent. The general conclusion as to the origin and source of the 
nitrates is sustained by a comparison of analyses of the soluble por- 
tions of (i) subsoil from the surface above the Mammoth cave, (2) 
cavern earth from the subjacent part of the cave, (3) bat guano, and 
(4) cavern earth immediately below the bat guano. A comparison of 
bulk analyses of bat guano and cavern earth follows ; and it is sug- 
gested that the calcium phosphate of the latter cannot be referred to 
the former, since the insolubility of this salt makes it a necessary resid- 
uary product of the solution of limestone. Analyses show that the 
water dripping from the roofs of caves is not markedly different from 
ordinary sub-drainage waters. The nitrates and other soluble salts 
accumulate only in the earths of relatively dry caverns, or where the 
inflow of water does not exceed in amount the water removed by 
evaporation ; and numerous analyses show that all dry caves contain 
nitrous earths. Nitrates found under overhanging cliffs are of a sim- 
ilar origin — evaporation of water which has percolated through the 
soil ; and essentially the same explanation will fit the case where 
liitrates accumulate on the surface of a manure heap, through the 
joint action of capillarj' attraction and evaporation. w. o. c. 
