QUATERNARY PERIOD. * 732 



re-elevation of the tract to its present height. But if the 

 land rose in the second continental period no more than 600 

 feet above the present level, this .... would have taken 

 another 24,000 years; the whole of the grand oscillation, 

 comprising the submergence and re-emergence, having taken, 

 in round numbers, 224,000 years for its completion; and 

 this, even if there were no pause or stationary period, when 

 the downward movement ceased, and before it was converted 

 into an upward one." 



To the geologist these figures, large as they are, will have 

 no appearance of improbability. All the facts of geology 

 tend to indicate an antiquity of which we are but beginning 

 to form a dim idea. Take, for instance, one single formation 

 our well-known chalk. This consists entirely of shells and 

 fragments of shells deposited at the bottom of an ancient sea 

 far away from any continent. Such a process as this must be 

 very slow ; probably we should be much above the mark if we 

 were to assume a rate of deposition of ten inches in a century. 

 Now the chalk is more than a thousand feet in thickness, 

 and would have required therefore more than 120,000 years 

 for its formation. The fossiliferous beds of Great Britain as 

 a whole are more than 70,000 feet in thickness, and many 

 which with us measure only a few inches, on the continent 

 expand into strata of immense depth ; while others of great 

 importance elsewhere are wholly wanting with us, for it is 

 evident that during all the different periods in which Great 

 Britain has been dry land, strata have been forming (as is, 

 for example, the case now) elsewhere, and not with us. 

 Moreover, we must remember that many of the strata now 

 existing have been formed at the expense of older ones ; thus 

 all the flint gravels in the south-east of England have been 

 produced by the destruction of chalk. This again is a very 

 slow process. It has been estimated that a cliff 500 feet 

 high will be worn away at the rate of an inch in a century. 



