XXVlll PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



such conditions, perhaps, some of the harder remains of land animals, 

 even of successive geological times, might occasionally be mingled 

 with those of the marine creatures existing around the land as it be- 

 came submerged. When we consider the effects which would be pro- 

 duced upon lands gradually sinking beneath the sea, and more espe- 

 cially when such lands are volcanic, we at once perceive the small 

 chance of preserving any large portion of the loose materials, with or 

 without animal and vegetable remains, in the state in which they 

 may have occurred on such dry land. Curious associations of rocks 

 might result from the harder parts of a volcano, those formed of 

 various lava currents, remaining, while the softer portions, such as 

 ashes and cinders, were removed by the breakers, new marine accu- 

 mulations intermingling with the old lava currents. Should the sea 

 again cover the Great Desert of Northern Africa, its sands would be 

 remodelled into beds, and would contain, intermixed with them, such 

 bones of men, camels and other animals as were sufficiently hard 

 to resist the friction of the breakers until they were buried in the 

 new marine beds with the remains, perhaps, of the marine creatures of 

 the time. In such cases, as also in those of volcanos, there would be 

 little trace of the old tracts of dry land, the portions of the latter 

 preserved being chiefly beds, such as limestone, more or less consoli- 

 dated from having been formed in lakes, rivers, or as subaerial tra- 

 vertine, and lava currents or other ejections of molten rocks upon 

 the land, these latter, when covered by deposits formed in water, 

 showing no traces of having been so thrown out on dry land, although 

 sometimes the pumice character of such rocks, however the vesicles 

 may be now filled up by solid matter infiltrated into them, may lead 

 us to suspect that they may have been vomited upon dry land. 



Mode in which Mineral Matter has been accumulated at previous 



Geological times. 



Mr. Darwin, in his paper *' on the Transportal of Erratic Boulders 

 from a Lower to a Higher Level," after noticing the facts seen in va- 

 rious European and American localities, and which appear to show 

 that such transportal had actually taken place, and after quoting the 

 observations of himself. Prof. John Phillips, Mr. Hopkins, Mr. 

 Maclaren, Mr. D. Milne, the Rev. J. G. Gumming, Mr. Mallet, 

 Prof. Hitchcock, and Dr. Buckland, takes into consideration certain 

 causes which have been thought to have produced this distribution of 

 boulders at higher levels than the supposed parent rock is now known 

 to occupy. After admitting that the destruction of rocks in some 

 localities may have been such, that fragments from them may have 

 been detached and drifted, when portions of them, since removed, oc- 

 cupied higher levels than they now do, levels sufficiently high to ac- 

 count for the removal of boulders to those places where they are now 

 found, and having also taken into consideration the value of unequal 

 elevations of parts of land since the boulders were dispersed, Mr. 

 Darwin proceeds to investigate the effects which would be produced 

 by coast ice upon a land gradually sinking beneath the level of the 

 sea. He adverts to the transportal of boulders by glaciers and coast 



