THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE IV. VOL. V. 



No. XI.— NOVEMBER, 1898. 



OS,IC3-IZNr.A.IL -A.iaTIGL:ES. 



I. — On Aggregate Deposits, and their Eelations to Zones. 



By the Eev. J. F. Blaice, M.A., F.G.S. 



[A paper read at the meeting of the British Association in September, 1898.] 



GEOLOGICAL time, like all other kinds of time, can only be 

 measured by the succession of events. If the events con- 

 sidered are constant in their recurrence and uniform in their 

 nature, their number will afford the means of measuring the 

 length of time. Thus the oscillations of a given pendulum, the 

 rotation of the earth on its axis, and its revolution round the sua 

 are sufficiently constant and uniform to afford a basis for our 

 seconds, days, and years. Of such uniform and constantly 

 recurring events geology affords no examples by which we could 

 measure the length of geological time. 



If, on the other hand, we consider a number of consecutive 

 events as terms of a series, we* obtain a scale by which to fix 

 the epoch or moment of occurrence of any other event. The 

 terms of this series may be all alike, as the years of a calendar ; 

 or they may be recurrent, like morning, noon, and night ; or 

 all different, as the succession of monarchs on a throne. Only 

 in the first of these cases can we expect the scale to be of 

 universal application ; in the others we know that the morning 

 at one place may be noon at another, and night at a third ; 

 while the dynastic succession in one country has no relation to 

 that in another. Now geology supplies us with time-scale events 

 of the two latter kinds only, and we cannot, therefore, expect 

 that the chronology founded on them shall be of universal applica- 

 tion — though the wider the application the better the chronology. 



The events the succession of which has been applied to establish our 

 geological chronology have been of two kinds — (1) the deposition of 

 strata ; (2) the development of the fauna, or in some cases the flora. 

 The use of the former is the stratigraphical, that of the latter 

 is the paleeontological method. It would be very wrong, in my 

 opinion, to put these two methods into antagonism with each other, 

 and to argue in favour of one or of the other : they ought never to 

 be divorced. It is as unscientific and misleading to say that the 

 nature of the deposit is of no consequence as it would be to disregard 



DECADE IV. VOL. V. NO. XI. 31 



