82 
The American Geologist. 
Feb. 1890 
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strata of thet rue gruuwackt' of German min- 
eralogists. ]>ut whilst this system contains 
no such beds, it is underlaid and sometimes 
indiscordant stratificatton, by a vast series of 
slaty rocks, in which much genuine grauwacke 
is exhibited. It is therefore manifest that if 
used at all in geological nomenclature, the term 
"grauwacke." must be ejected as inapplicable 
to the first great system below the old red 
sandstone, and restricted to rocks which 
were noio proved to be of much higher anti- 
quity. My friend Professor Sedgwick will 
doubtless soon dispel the obscurity which 
hangs over these grauwacke rocks, with 
which his labors in Wales and Cumberland 
have so well enabled him to grapple. 
To return, however, to the system under re- 
view, I was urged by leading geologists both 
at home and abroad to propound an entirely 
new name for it. In consonence, therefore, 
with those views which have rendered the 
names used by English geologists so current 
throughout the world, I venture to suggest, 
that as the great mass of rocks in question, 
trending from southwest to northeast, travers- 
es the kingdom of our ancestors the Silures, 
the term "Silurian system" should.be adopted 
as expressive of the deposits which lie between 
the old red sandstone and the slaty rocks of 
,^ Wales, including, as above detailed, the Lud- 
"S _, low, Wenlock, Caradoc aud Llandeilo forma- 
"ox."^ tions. One of the largest of these formations, 
'ticS" to which, indeed, the Llandeilo flags are fre- 
quently subordinate, has been named after 
the bold and picturesque ridge of Caer Caradoc 
in Shropshire. 
I further propose that the system be sub- 
divided into "Upper" and "Lower Silurian 
rocks," the former embracing the deposits of 
"Ludlow" and "Wenlock," the latter those of 
"Caradoc" and "Llandeilo." Bythis arrange- 
-^':5^ment the observer will not be embarrassed 
's ^ when he finds that certain typical strata have 
^ disappeared. Thus, for instance, when the 
'-^ zones of limestone thin out, by which the 
formation of Ludlow and Wenlock are sub- 
divided, it is no longer practicable to mark 
lines of separation between them. Under 
such circumstances the united mass will sim- 
ply be described as "Upper Siluran rocks,' 
whilst wherever similar causes prevent the 
separation of the "Caradoc sandstones" from 
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