Vol. 67.] ANNIVERSARY ADDRESS OF THE PRESIDENT. lxxix 



present inviting spots for deep borings, if funds could be found for 

 carrying them out, not only for economic but for strictly scientific 

 reasons. Thus, borings in the north of the Isle of Man, made in 

 search of salt-deposits, have revealed what was, until Pleistocene 

 times, part of the bed of the Irish Sea ; and we can hardly avoid 

 speculating as to what would have been found if it had been prac- 

 ticable to carry down the Funafuti boring twice as far as was 

 possible under the circumstances. 



A consideration of the fact that each formation has been derived 

 from, and implies the destruction of, an equal mass of pre-existing 

 formations makes it evident that much of what would have been 

 extremely valuable in giving evidence of palseogeography has been 

 irrecoverably destroyed. Beyond the average line of outcrop of 

 each formation we only have left occasional fortunate extensions 

 of it, or just the stranded outliers which happen to have escaped 

 destruction. In the absence of these we are driven to do our 

 best with bits broken from the edges of the formations, which 

 may chance to have been embedded in later rocks and to be still 

 recognisable. 



In default of other evidence, we may be guided by the principle 

 that parallelism in the bedding of closely associated strata implies 

 that any movement which may have occurred during their depo- 

 sition has been of an epeirogenic character. There may have been 

 advance or retreat of coast-lines, but no development of striking new 

 structures. The physiographic features will remain approximately 

 parallel to one another during the time and at the place represented 

 by a series of conformable deposits. It is on this assumption that 

 we are able to draw inferences as to the probable position and 

 trend of the shore-lines of the Liassic Sea, based on our knowledge 

 of the extension of the Trias on the one hand and of the Lower 

 Oolites on the other. 



(b) Growth of Britain. 



From fragments of evidence like this, hammered out bit by bit 

 by himself or by many other observers, Mr. Jukes-Browne has 

 made a brave struggle to picture for us the stages of geography 

 through which Britain has advanced to its present configuration, 

 its successive ' lines of growth,' and the normal and critical periods 

 of its evolution. 



That so much success has rewarded the attempt is to some extent 

 due to the nature of the area chosen. Britain, though at the present 

 time the north-western outpost of the European continent, has not 



