44 
Case 4C. — Specimens illustrating effects of erosion by wind 
and water, also stages and forms of rock weathering. Ripple 
marked surfaces of exceptional size and degree of perfection. 
Surfaces showing mud cracks and rain drops. “Slickensided” 
surfaces. 
Case 5, — Large specimens of types already mentioned. 
They include two septaria three feet in diameter, a surface four 
feet square showing cross ripple-marks, large glaciated surfaces 
from the well-known Kelly’s Island, Ohio, locality, and others. 
Upon the wall are framed specimens of the so-called ruin 
marble, a rock in which the natural faulting and coloring has been 
such as to give to the slab an appearance like a painting of a 
ruined city. 
Pedestal 6 . — Surface of sandstone, three by four feet, show- 
ing ripple-marks, from Berea, Ohio. 
Pedestal 7, — Collection of basaltic columns from the Giant’s 
Causeway, Ireland, and the Rhine Valley. The grouping of these 
is intended to illustrate the stair-way arrangement which usually 
characterizes cliffs of basalt. The columns are entirely of natural 
formation, being produced by the shrinkage of the basalts from 
cooling. 
In Hall 66 will be found specimens of lava from the Italian 
and Hawaiian volcanoes. Specimens illustrating veins and their 
formation. Also rock faulting, folding and texture. 
HALL 66. 
LITHOLOGY. 
The collections shown in this Hall aim to illustrate the dif- 
ferent varieties of rocks as they are known to petrographers and 
also to exhibit the characteristics of these rocks and their order of 
succession as they appear in different localities. 
About 2,000 specimens are shown, most of them being of the 
uniform size adopted by petrographers — 3 x 4 x i inch. 
The specimens are classified under the heads of Eruptive, 
Aqueous and Metamorphic rocks. The Eruptive rocks are those 
which have been formed at great depths, and were once in a state 
of igneous fusion. Being most deeply seated they may be con- 
sidered to be the primary rocks of the earth’s crust, so far as it is 
