Burbank.] : 162 [April 17, 
tion I have found that Prof. Agassiz has long been convinced that 
our domesticated species was a mixture of two stocks, one derived 
from the Felis maniculata Riippel, the other the Felis catus L. 
Mr. L. 8. Burbank gave an account of the exploration of 
the Mammoth Cave by a party of geologists and naturalists 
from the meeting of the American Association at Indianapo- 
lis, last August. 
The observations made by the zoologists of the party had been 
fully reported in the American Naturalist. He had’ studied more 
particularly the peculiar mineral forms, which, in great variety and 
beauty, adorn -certain portions of the cave. Among them those 
resembling vines, flowers and wreaths are most conspicuous, and 
have often been spoken of as almost miraculous in the beauty and 
accuracy of their imitative character. They were, of course, all pro- 
duced by natural causes, and these causes are not difficult to trace. 
‘ Although these forms all consist of gypsum or sulphate of calcium, 
there is no massive gypsum in the rock formation of the cave. It 
appears only in a fibrous shape, filling cracks and fissures, and as an 
efflorescence on the surface of the limestone of particular strata, which 
do not appear near the entrance of the cave. The curved fibrous 
masses are first seen on the long route, beyond Echo River, nearly 
six miles from the entrance. They first appear on the surface of a 
stratum of the limestone, some six feet in thickness, which is ex- 
posed on the side of the cave. As the path descends, a point is soon 
reached where this stratum forms the roof, and here the crystalline 
forms appear in great variety. 
The portions of the rock where they are found contained originally 
a sulphide of iron or iron pyrites, which, on exposure to air and moist- 
ure, becomes oxidized, and forms sulphuric acid and an oxide of iron. 
The sulphuric acid decomposes the limestone and forms the gypsum, 
which, being soluble, is carried by eo water to the surface, where it 
crystallizes. 
The various forms are not produced, like stalactites, by a deposit 
from dripping water containing the mineral matter; they are devel- 
oped from within. The deposits first made at the surface are in- 
creased by additions from beneath, which continually push out the 
parts first deposited, and by unequal pressure and adherence to the 
surrounding rock the curved forms are produced. Along lines of 
fracture the curved, leaf-like masses are thrown ont in great abun- 
dance and variety. ‘The rosette form results from the decomposition 
