Gallery XT. 
Between 
Wall-eases 
6 & 7 . 
Wall-case 
6 a and 
adjoining 
pillar. 
12 GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. 
DYNAMICAL SERIES; TRACKS AND MARKINCS. 
At tlie further end of tlie (Tallery are e.xhibitetl several 
illustrations of forms produced by natural agencies, as a rule 
unconnected with animal or ve<fetable life, and yet frequently 
simulating fossil organisms. Some of these illustrate the 
greater geological agents. The kind of movement that 
takes place in mountain building is shown by some models 
constructed by Lord Avebury and presented by him (see 
Quart. Journ. Geological Society, li.\, p .348, and Ixi, p. 345). 
Movements of this kind naturally crumple and contort the 
rocks, and fragments bent and folded in this way are 
exhibited in the adjoining Wall-case. Besides crumpling, 
there is a shearing action, and in some of the slates may 
be observed tiilobites greatly distorted, proving the considei- 
able movement that the particles of rock have undergone 
The specimens of “ruin marble” below are also due to 
slight cracks and displacements of the original rock-bands, 
a phenomenon even more clearly exemplified in a brightly 
coloured rock from Johannesburg. The “landscape marble” 
underneath, also proliably owes its origin to subsequent 
disturbance of the original strata, in some cases perhaps 
combined with the action of organisms. Earth-movements 
acting on less compact rocks, such as those containing 
pebbles or boulders, frequently produce a striation and 
facetting of the stones, as exemplified in some curiously 
facetted pebbles f)f Ciirboniferous age foimd in the Punjab. 
One of these is here exhibited. Beside it are boulders or 
pebbles polished or striated or facetted, either by the action 
of ice or by that of wind-blown sand, or even by animals 
rubbing against them. There are also shown examples of 
rock-weathering by other agencies, such as atmospheric 
weathering, and borings by laud-shells, sea-shells such as 
Fholas ami SaAcava, worms, sponges, white ants, and other 
organisms. Among these specimens the most interesting is 
a portion of one of the columns of the temple of Jupiter 
Serapis at Puzzuoli, familiar to all readers of Lyell’s “ Prin- 
ciples of Geology.” The marble has been perforated by 
boring marine .shells (Lithodomns), which attacked it at a 
time when, owing to the subsidence of the land, the temple 
had been submerged more than 20 ft. beneath the sea. The 
floor of the temple was originally 15 ft. above the level ot 
the sea, and, since submergence, has again been raised to 
about its original level. 
