* DEVONIAN AND SILURIAN STRATA. 67 
rences, by which the carboniferous and Dyassic forma~ 
tions were evolved, are accordingly (reading from above 
downwards) : 
5. Dcep Sea.| Marine Mountain Marine Magnesian 
forms. Limestone. animals, | Limestone. 
4. Subsidence, Littoral | Conglome- Red Sand- 
beneath the, forms. rate and stone. 
Sea, Sandstone. Dyas. 
3-Quiescence.) Freshwater Coal Terrestrial | Coal mea- 
and measures, plants. sures, Red 
Marsh forms. : Sandstone, 
Coal fields. 
2. Upheaval, Littoral | Conglome- Millstone 
above the' forms. rate and grit. Carhonife- 
Sea. Sandstone. tous forma- 
tion. 
x. Deep Sea.| Marine Mountain Marine Carbonife- 
forms. Limestone. animals. rous Lime- 
stone. 
From this account it is also manifest that in cascs of 
incomplete elevation, such as took place in North 
America, the formation of the middle period is either 
disturbed or totally omitted, and that it may depend on 
local causes and the duration of the oscillations if, 
as in the Russian Permian formations, corresponding to 
the German Dyas, the boundaries of the subdivisions 
are more or less obliterated. 
The two series of strata beneath the mountain lime- 
stone, and reaching the depth of more than 3000 and 
6000 metres, the Devonian and Silurian formations, 
are the lowest, and therefore the first which clearly 
bear the mark of their origin as marine deposits. Both 
