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‘ 
Part II. Secr.i.§1.] CAMBRIAN. 649 
The prevailing absence of limestones from the Cambrian system 
is accompanied by a failure of the foraminifera, corals, and other cal- 
careous organisms which abound in the limestones of the next great 
geological series. The character of the general sandy and muddy 
sediment must have determined the distribution of life on the floor 
of the Cambrian sea, and doubtless has also affected the extent of the 
final preservation of organisms actually entombed. 
The plants of the Cambrian period have been scarcely at all 
preserved. That the sea then possessed its sea-weeds can hardly be 

Fic. 319.—Grovup oF CAMBRIAN (PRIMORDIAL) TRILOBITES.? 
1, Olenus impar (Salt.) (enlarged); 2, Paradoxides Davidis (Salt.) G); 3, Cono- 
coryphe (?) Williamsoni (Belt.); 4, Ellipsocephalus Hoffi (Schloth.); 5, Agnostus 
princeps (Salt.) (enlarged); 6, Microdiscus sculptus (Hicks) (enlarged); 7, 
Agnostus Barlowii (Belt.) (enlarged); 8, Hrinnys venulosa (Salt.); 9, Plutonia 
Sedgwickii (Salt.); 10, Agnostus cambrensis (Hicks) (and enlarged); 11, Dikelo- 
cephalus celticus (Salt.). 
doubted, and various fucoid-like markings on slates and sandstones 
(eg. the “‘fucoidal sandstone ” of Sweden) have been referred to the 
vegetable kingdom. The genus Kophyton from Sweden, and others 
from the Potsdam sandstone of North America, have been described, 
but some of these are probably worm-tracks, others are merely 
imitative wrinkles and markings of inorganic origin, and it is not 
certain that any of them are truly plants. What has been regarded 
as an undoubted organism occurs in abundance in the Cambrian 
* Where not otherwise stated the figures are of the natural size. 
