173 



^lexihle sandstone, India. — Elexible sandstones and limestones 

 have been found in several parts of the world ; they bend some- 

 what like a sheet of thick india-rubber. 



Cone-in-cone structure. — A curious structure found in shale at 

 Picton and elsewhere. 



jRiiyple-marJcs. — The ripples made by the waves of the sea upon 

 an ancient beach. A large slab from Pyrmont quarries is placed 

 near the Sydney case. Eipple-marks are very common in the rocks 

 round Sydney. 



Geodes. — Hollow masses of chalcedony, &c., sometimes lined 

 internally with crystals. Grood specimens from Illinois. 



Interhedding of volcanic tuff with clay stone. Also the same 

 tuff jumbled together with radiolarian chert. — Both from 

 Tamworth. 



Intrusion of volcanic agglomerate by igneous rock, Moonbi 

 Sange. — The fragmental character of the agglomerate is well 

 brought out by the weathering it has undergone. 



Intrusion of diorite by granite, Juuee. — A large slab showing 

 well the intrusion of one igneous rock by another (Plate VIII). 



Bone Breccia, Wellington Caves. — The accumulated remains 

 of animals, frequently extinct, that have occupied the Caves. 



SlicJcensides. — The walls and other portions of mineral lodes Structures due 

 P . J. 1 1 • 1 1 ^ 1 n J. o 1 . to Movements 



are often round polished and grooved, due to one surface having of the Rock 



moved over another. Specimens of slickensided coal, galena, ^'^tlii" tlie 



^ . . . Earth's Cnist. 



quartz, ironstone, pyrites, quartz-felsite, calcite, and flucan will 



be found in cases 112, 113, and 133. In some of these a fine 

 film of gold has been deposited over the slickensided surfaces at 

 a later date. 



Distortion, sTiearing, crt(,s]iing,C^^Q 112. — Pebbles from a con- 

 glomerate at Gruudagai have been flattened and sheared (that is, 

 one portion displaced relatively to the rest) by the intense 

 pressure to which the rock has been subjected. Prom Barmed- 

 mau pebbles from a similar conglomerate have been not only 

 distorted in this way, but have been pressed together with such 

 force that one has been indented bv the other. The best 



