Geological Society of London, 131 



2. " The Physical Conditions under which the Upper Sihirian and 

 succeeding Palasozoic Kocks were probably deposited over the 

 Northern Hemisphere." By Henry Hicks, Esq., F.G.S. 



In this paper the author, after pointing out the lines of depression 

 explained in his former paper to the Society, now further elaborated 

 the views then propounded by him by carrying his examination into 

 the higher Palgeozoic series and into more extensive areas. Beginning 

 at the top of the Lower Silurian, where he first recognizes any 

 evidence of a break in the Palaeozoic rocks, he proceeded, to show 

 that this break was restricted to very limited areas, and almost en- 

 tirely confined to the parts which had been first submerged, and 

 where the greatest thickness of sediment had accumulated on both 

 sides of the Atlantic, and hence where the pre-Cambrian crust had 

 become thinnest. On the European side this break occurred where 

 volcanic action had taken place, and has doubtless to be attributed to 

 the combined action of upheaval of portions of the crust and the 

 heaping up of volcanic material, the latter in some cases forming 

 volcanic islets of considerable extent. He strongly objected to look 

 upon these breaks, even in the British area, where they are most 

 marked, as evidence of a want of continuity over other and far greater 

 areas ; or to admit that even where there was conformity in the rocks 

 at this point, '-^ great intervals of time are indicated, unrepresented by 

 stratified formations." The conformity found in extensive and widely 

 separated areas is proof also that a gradual contraction took place of 

 an enormous portion of the crust in the northern hemisphere in 

 Palaeozoic times ; and the breaks at the close of the Lower Silurian 

 and in the Devonian are not indications of an arrest in the general 

 subsidence. After indicating the changes which must have taken 

 place in the climate from this gradual spreading of the water and the 

 evidence to be derived from the consideration of the deposits and the 

 faunas, the author drew the following general conclusions : — 



1. That the condition of the northern hemisphere at the beginning 

 of Palgeozoic time was that of immense continents in the higher lati- 

 tudes, traversed by mountainous ranges of great height, but with a 

 general inclination of the surface, on the one side (European) to the 

 south-west and south, and on the other side (American) to the 

 south-east and south. 



2. That these continents were probably covered, at least in their 

 higher parts, with ice and snow ; and that much loose material had 

 consequently accumulated over the plains and deeper parts, ready to 

 be denuded off as each part became submerged. This would account 

 for the enormous thickness of conglomerates, with boulders, grits, 

 and sandstones, found in the early Cambrian rocks, and also to a 

 certain extent for their barrenness in organic remains. 



3. That the depression over the European and American areas 

 was general from at least the latitude of 30° northwards ; that the 

 parts bordering the Atlantic were the first to become submerged ; 

 the lower latitudes also before the higher. 



4. That the depression could not have been less altogether, for 

 the whole of the Palasozoic, than 50,000 feet; and that conform- 



