Professor J. E. Marr— Address. 473 



several parts of the world, but much more information must be gathered 

 together before our restorations of ancient sea-margins approximate to the 

 truth. The Carboniferous rocks of Britain have been specially studied with 

 reference to the distribution of land and water during the period of their 

 accumulation, and yet we find that owing to the erroneous identification of 

 certain rocks of Devonshire as grits or sandstones, which Dr. Hinde has 

 shown to be radiolarian cherts, land was supposed to lie at no great 

 distance south of this region in Lower Carboniferous times, whereas the 

 probabilities are in favour of the existence of an open ocean at a consider- 

 able distance from any land in that direction. This case furnishes us with 

 an excellent warning against generalization upon insufficient data. 



As a result of detailed study of the strata, the effects of earth- movements 

 have been largely made known to us, especially of those comparatively 

 local disturbances spoken of as orogenic which are mainly connected with 

 mountain-building, whilst information concerning the more widely-spread 

 epeirogenic movements is also furnished by a study of the stratified 

 rocks. The structure of the Alps, of the North-West Highlands of 

 Scotland, and of the uplifted tracks of North America is now familiar to 

 geologists, whilst the study of comparatively recent sediments has 

 proved the existence of widespread and extensive movements in times 

 which are geologically modern ; for instance, the deeo-water deposits 

 of late Tertiary age found in the West Indies indicate the occurrence 

 of considerable uplift in that region. But a great amount of work 

 yet remains to be done in this connection, especially concerning 

 horizontal distortion of masses of the earth's crust, owing to more rapid 

 horizontal advance of one portion than of another, during periods of 

 movement. Not until we gather together a large amount of information 

 derived from actual inspection of the rocks shall we be able to frame 

 satisfactoiy theories of earth-movement, and in the meantime we are 

 largely dependent upon the speculations of the physicist, often founded 

 upon very imperfect data, on which is built an imposing superstructure 

 of mathematical reasoning. We have been told that our continents and 

 ocean-basins have been to a great extent permanent as regards position 

 through long geological ages ; we now reply by pointing to deep-sea 

 sediments of nearly all geological periods, which have been uplifted from 

 the ocean-abysses to form portions of our continents ; and as the result 

 of study of the distribution of fossil organisms, we can point almost 

 as confidently to the sites of old continents now sunk down into the ocean 

 depths. It seems clear that our knowledge of the causes of earth- 

 movements is still in its infancy, and that we must be content to wait 

 awhile, until we have further information at our disposal. 



Recent work has proved the intimate connection betwixt earth- 

 movement and the emission and intrusion of igneous rocks, and the study 

 of igneous rocks has advanced beyond the petrographical stage ; the rocks 

 are now made to contribute their share towards the history of different 

 geological periods. The part which volcanic action has played in the 

 actual formation of the earth's crust is well exemplified in Sir Archibald 

 Geikie's Presidential Addresses to the Geological Society, wherein he treats 

 of the former volcanic history of the British Isles. 1 The way in which 

 extruded material contributes to the formation of sedimentary masses has, 

 perhaps, not been fully grasped by many writers, who frequently seem to 

 assume that deposition is a measure of denudation, and vice versa, whereas 

 deposition is only a measure of denudation, and of the material which has 

 been ejected in a fragmental condition from the earth's interior, which 

 in some places forms a very considerable percentage of the total amount 

 of sediment. 



1 Sir A. Geikie, Quart. Joum. Geol. Soc, vols, xlvii and xlviii. 



