﻿lxiv PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. [May I905, 



meteorologist has his chronometer with which to separate one set 

 of synchronous events from the next ; the geologist can only attempt 

 to draw chronometric lines by careful study of the tracings of the 

 geogram. I mention this obvious fact, because it appears to me that, 

 notwithstanding its obviousness, there is a tendency to compare the 

 lines of the tracings with the chronometric lines. 



If the meteorologist had no chronometer, but merely a set of 

 continuous records traced on paper which had moved at uniform 

 speed, he would be able, in dealing with some of the records, to 

 construct a time-scale by observation of the tracings themselves. 

 Merely -local changes in the direction of the wind or in the amount 

 of rainfall would throw little light on this subject, but he would 

 soon find that there were diurnal and annual variations in the 

 changes of air-pressure and of temperature, and by means of the 

 latter especially he would be able to divide the strips recording the 

 traces into lengths corresponding with day and night, and with 

 summer and winter. Even if the paper on which the tracings had 

 been recorded had not moved at uniform speed, this could be done, 

 although, in this case, the length of the paper containing the records 

 of one day would differ from that of the paper containing those of 

 another. 



The more widespread the meteorological changes thus recorded, 

 the more useful would they be found for establishing a time-scale, 

 those of the greatest utility being due to extra-terrestrial, and not 

 merely to geographical, causes. 



By means of these widespread meteorological changes we could, 

 if we had a series of meteorograms from various parts of the world, 

 beginning simultaneously at each part, construct a time-scale 

 which would enable us to correlate as regards date, minor changes 

 which had occurred in widely-distant regions. But, apart from 

 these, correlation of events could also be made in the case of less 

 widely-distant regions, by using records of less widespread, though 

 not purely-local character. Similar records in some cases would 

 not be due to events happening quite simultaneously in two tracts, 

 as, for instance, in the case of an advancing storm-area; these, 

 however, would not seriously confuse the skilled meteorologist. 

 1 INow, this is very much the state of affairs as affecting the 

 geologist, when concerned with the study of geograms. Having no 

 chronometer, he must use the tracings on the geogram to establish 

 his time-scale. The records of the geograms are not made at a 

 uniform rate, and one of the tasks which confronts him is the 

 endeavour to discover any periodicity of occurrence of certain events 



