80 THE DEVONIAN AND CARBONIFEROUS. [bull. 80. 



boniferous system consists of, first, the upper part of the Old Red sand- 

 stone resting upon lower beds of Old lied sandstone, u neon form ably 

 about the Cheviot Hills, or upon the Cheviot Volcanic series, or upon 

 Silurian rocks, as in Northumberland. The second formation, rest- 

 ing conformably upon the first, is the Mountain or Carboniferous lime- 

 stone. The third member of the series is the Millstone grit and shales. 

 The fourth, the Coal Measures, including the familiar coal fields of 

 Lancashire and Cheshire, of Yorkshire, Northumberland, and Derby- 

 shire ; these latter are terminated where contacts are seen by the " New 

 Red," in some places apparently conformably, but generally uncon- 

 formably. The system in this Pennine range was evidently terminated 

 both below and above by geologic disturbance of greater or less extent, 

 furnishing natural deliminations, thus peculiarly fitting it for a stand- 

 ard of geologic definition. 



An analysis of the standard systems in geologic classification shows us 

 that a system is a series of rock formations whose stratigraphic order 

 and lithologic composition are thoroughly well expressed in some defin- 

 able geograpic region, and whose fossils indicate a continuous biologic 

 sequence, more or less distinctly broken at its lower and upper limits 

 from contiguous formations. Thus a typical section has definite geo- 

 graphic position, geologic delimitation, and biologic definition. The 

 Silurian system in Wales and western England, the Devonian system 

 of south and north Devonshire, the Jurassic system of the Jura Moun- 

 tains, are examples, and no less perfect is the Pennine Carboniferous 

 system of the Pennine range of north England to which the unsatisfac- 

 tory name of Carboniferous has been so long applied. 



While so much is true of the standard or typical expression of a geo- 

 logic system, it can not be expected that any system will offer precisely 

 the same features in other regions of the world or on other continents. 

 We conclude, therefore, that: (1) Because the composition, the size of par- 

 ticles, and the order and thickness of deposits are all determined by 

 conditions that are geographically dissimilar, therefore a geologic sys- 

 tem can have but one typical geographic position ; (2) because the geo- 

 logic events, such as elevation of land, breaking of strata recorded in 

 faults, and volcanic eruptions, do not take place either uniformly or 

 simultaneously in different parts of the earth, it is certain that intervals 

 or breaks in sedimentary formations will not be uniform for separate 

 regions j and (3) because organisms in the past can not be regarded as 

 having ceased to carry on the ordiuary functions of life and reproduc- 

 tion, all the breaks in the sequence of organisms, all the sharp lines dis- 

 tinguishing the faunas or floras of one formation from those of a pre- 

 ceding or following formation, are local and not universal. 



To apply these reflections to the present case, it will be seen that the 

 settlement of the question as to which is the typical section upon which 

 the Carboniferous system was founded, will greatly facilitate all attempts 

 to determine the limits of the system in other regions. It is evident 



