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312 DYNAMICAL GEOLOGY. [Book IT. 
rocks and escape observation. Daubrée has imitated experimentally 
indentations produced by the contiguous portions of conglomerate 
pebbles.’ 
In discussing the cause of these indentations it must be re- 
membered that imprints of pebbles upon each other, particularly 
when the material is limestone or other tolerably soluble rock, may 
have been to some extent produced by solution taking place most 
actively where pressure was greatest. But there are other 
indubitable evidences of actual deformation within the mass of a 
rock, proving a certain degree of mobility even in what would be 
termed solid and brittle rocks. Of these evidences, perhaps the most 
instructive and valuable are furnished by the remains of plants and 
animals occurring as fossils. Where fossiliferous rocks have under- 
gone great compression, and have suffered internal rearrangement, 
the extent of this movement can be measured in the resultant 
distortion of the fossils. In Figs. 77 and 79 drawings are given of two 

= 
Z, 

BZ 
Yj 
G 
Fic. 77.—A TRrILOBITE Fic. 78.—THE same Fic. 79.—A  Bracuiopop 
(Calymene Blumen- TRILOBITE, ALTERED (Strophomena expansa), 
bachii), NATURAL BY DEFORMATION— NATURAL SHAPE, 
SHAPE. Lowrer _SILuRIAN, 
HENDRE WEN, NEAR 
Crrrig Y Drvurpion, 
Norru Wa tzs. (B.) 
Lower Silurian fossils in their natural forms. In Fig. 78 a specimen of — 
the same species of trilobite as in Fig. 77 is represented where it 
has been distorted during the compression of the enclosing rock. 
In Fig. 80 four examples of the same shell as in Fig. 79 are 
shown greatly distorted by a strain which has elongated the rock in 
the direction a b. 
Another illustration of the effects of pressure in producing 
deformation in rocks, is supplied by the so-called “lignilites,”’ 
' Comptes Rendus, xliv. p. 823; also his Géologie Hapérimentale, Part I. sect. ii. 
chap. iii. where a series of important experiments on deformation is given. For various 
examples and opinions, see Rothpletz, Z. Deutsch. Geol. Ges. xxxi. p. 355. Heim, 
Mechanismus der Gebirgsbildung, 1878, vol. ii. p. 31. Hitchcock, Geology of Vermont, 
i. p. 28. Proc. Bost. Soc, Nat. Hist. vii. pp. 209, 353; xviii. p. 97; xv: p. 1; xmas 
Amer. Assoc, 1866, p. 83. Amer. Journ. Mei (2)\xxxi..p. 372, 
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