Notices of Memoirs — Prof. Lapivorth's Address. 419 



can always distinguish three stages : first, the stage of erosion and transportation, 

 in which the rocli fragments were worn off the rocks of the higher ground and 

 washed down by rain and rivers to the sea ; second, a stage of deposition and 

 consohdation below the surface of the quiet waters ; and third, a final stage in 

 which the completed rock-formation was bent and upheaved, in part at least, into 

 solid land. In the formations of the organic type three corresponding stages are 

 equally discernable : first, the period of mineral secretion by organized beings ; 

 second, the period of deposition and consolidation ; and third, the final period of 

 local elevation in mass. But one and all, mechanical and organic alike, they bear 

 in their composition, in their arrangement, and in their fossils, abundant and 

 irresistible evidence that they were the products and that now they are the 

 memorials of the physical geography of their time. 



Guided by the principles of Hutton and Lyell, geologists have worked out with 

 great care and completeness the effects of those agencies which rule in the first of 

 these three life-stages in the history of a mechanical formation. No present 

 geological processes are more familiar to the young geologist than those of 

 denudation, erosion, and transportation. They form together the subject-matter 

 of that most wonderful fascinating chapter in geology which from its modest 

 opening among the quiet Norfolk Sandhills sweeps upwards and onwards without 

 a break to its magnificent close on the brink of the gorge of the Colorado. But 

 our knowledge of the detailed processes of deposition and consolidation which rule 

 in the second stage is still exceedingly imperfect, although a flood of light has 

 been thrown upon the subject by the brilliant results of the Challenger Expedition. 

 And we are compelled to admit that our knowledge of the operations of those 

 agencies which rule in the processes of upheaval and depression is as yet almost 

 nil ; and what little we have already learnt of the effects of these agencies is the 

 prey of hosts of conflicting theories that merely serve to annoy and bewilder the 

 working student of the science. 



But not one of the formative triad of detrition, deposition, and re-elevation can 

 exist without the others. No detrition is possible without the previous upheaval of 

 the rock-sheet, from which material can be removed ; no deposition is possible 

 without the previous depression of the rock-sheet, which forms the basin in which 

 the fragmentary material can be laid down. 



Our knowledge, therefore, of the origin and meaning of any geological formation 

 whatever can at most be only fragmentary until this third chapter in the life-history 

 of the geological formation has been attacked in earnest. 



Now all the rich store of knowledge we possess respecting the first stage in the 

 life of a geological formation has been derived from a comparison of certain 

 phenomena which the stratigraphical geologist finds in the rock formations of the 

 past, with correspondent phenomena which the physical geographer discovers on 

 the surface of the earth at the present. And all that we know of the second stage 

 again has been obtained in precisely the same way. Surely analogy and common 

 sense both teach us that all which is likely to be of permanent value to us as 

 regards the final stage of elevation and depression must be sought for in the same 

 direction. 



Within the last twenty years or so many interesting and vital discoveries have 

 been made in the stratigraphy of the rock formations, which bear largely upon this 

 obscure chapter of elevation and depression. And I propose on this occasion that 

 we try to summarise a few of these new facts, and then, reading them in 

 conjunction with what we actually know of the physical geography of the present 

 day, try to ascertain how such mutual agreement as we can discover may serve to 

 aid the stratigraphical geologist in his interpretation of the true meaning of the 

 geological formations themselves. We may not hope for many years to come to 

 read the whole of this geological chapter, but we may perhaps modestly essay an 

 interpretation of one or two of the opening verses. 



In the physical geography of the present day we find the exterior of our 

 terraqueous globe divided between the two elements land and water. We know 

 that the solid geological formations exist everywhere beneath the visible surface of 

 the lands, but of their existence under the present ocean floor we have as yet no 

 absolute certainty. We know both the form of the surface and the composition of 

 the surface of the continental parts of the lithosphere ; we only know as yet even 

 in outline the form of its oceanic portions. The surface of each of our great 



