﻿Ixil PROCEEDINGS OE THE GEOLOGICAL SOCIETT. [May 1905, 



measurement ; and further, if we knew the rate of accumulation, we 

 should be in a position to discover the time taken for the formation 

 of the whole mass. Our classification would be purely arbitrary. 

 We might make a foot, or a yard, or 100 feet, our unit, and 

 separate the whole mass of sediment into a number of divisions of 

 equal value. 



Actually, however, we find that the sediments of any particular 

 period were not accumulated at the same rates in different areas, 

 and also that the sediments of different parts of the geological 

 column in one area are dissimilar, and that those of the corre- 

 sponding parts of the column in two areas may also be dissimilar. 

 If, then, we could obtain a mass of sediments constituting a 

 geological column in any area by sinking a gigantic bore to the 

 bottom of the column, and we were to lay that column flat, we 

 should be able to study the variation in the sediments of the column 

 as regards lithological characters and organic contents, reading 

 them off, say, from left to right. Such a column would bear some 

 resemblance to the meteorograms, or tracings of the meteorological 

 instruments, which are obtained in order to detect the weather- 

 changes in a place from time to time ; and we may find it useful to 

 institute a further comparison between these meteorograms and the 

 records of the geological columns of various parts of the world. 

 The latter, for the sake of simplicity, I propose to speak of in this 

 address as geograms. 1 



In a meteorogram we may have barograms, or lines representing 

 barometric oscillations ; thermograms showing changes of tempe- 

 rature ; anemograms recording variations in the direction and 

 velocity of the wind ; and lines recording the amount of rainfall. 

 Some of these are curved or zigzag, others broken lines. 



In the case of a geogram formed of a narrow column, most of 

 the lines, whether separating strata of different lithological characters 

 or those containing different assemblages of organisms, will be 

 practically parallel ; but if the geogram be wide, representing, say, 

 500 miles of the sedimentary column, the lines, like those of the 

 meteorogram, will be in some cases broken, in others zigzag. 



The two principal types of lines of a geogram will be those 



1 I here use this term, which is (in many respects) strictly comparable to that 

 of meteorogram, in place of the expression ' geological column,' for the latter 

 unconsciously leads one to imagine a thickness of sediment of small diameter. 

 A geogram may be of any width up to that of the circumference of the earth. 

 The term is, however, merely used for purposes of comparison : I do not 

 advocate its adoption. 



