TRANSACTIONS OF THE SECTIONS. 89 



period. Commencing the inquiry with reference to the American area, the extent 

 and range of the " Hamilton marine group " indicates tliat the relative position of 

 the coast-line, whence its materials were derived, was in the north and east 

 whilst the arrangement of all the subordinate members of that group point clearly 

 to thedirection of distribution having been south and west. 



In like manner the marine Devonian group has a well-defined northern boundary- 

 line across the Europeo- Asian region. Wholly wanting in Ireland, it is well exhi- 

 bited, in its early facies, in North Devon (Linton), next seen in the Boulonnais 

 and has been proved to underlie the Cretaceous formation of the north of France^ 

 as far as beyond LiUe and Tournay, from near which latter place it presents a 

 well-defined limit across Belgium eastwards. At Gembloux it is seen to have 

 been accumulated unconformably upon a much older Palteozolc series (Lower 

 Silurian). 



The fiu-ther extension of the " Devonian " sea-beds is concealed for a considerable 

 interval by Jurassic, Cretaceous, and Nummiditic gToups, but they reappear in the 

 mass of the Harz Moimtains, where, as in the Belgian sections, they present un- 

 conformity. 



The gradation of change, resulting from shallow to deeper water conditions, is 

 well marked m the Harz "Devonian" series, and hence may be inferred with cer- 

 tamty that the boundary-line lay to the north. Like considerations applied to the 

 Devonian depositions of Germany, to the south and east of the Ilartz, put that part 

 of Central Europe in the condition of sea, and place the boundary-line as trendino- 

 north-east, conforming to the mass of the old Scandinavian land, as from above 

 Magdebourgtothe Gulf of Eiga, and thence, by St. Petersburg, to the White Sea. 



From this, Its northern limit, the "Devonian" sea stretched southwards over 

 Devon and Cornwall, France, the north-east parts of Spain, and over North Africa • 

 eastwards, across Europe, to the shores of the Black Sea, into Central Asia (Altai) • 

 and we have its characteristic fauna from Thibet and China. ' 



The form of the continental area of the time is thus closely marked out. On the 

 Amencan side it lay, for the whole breadth of that region, as at present, with 

 an^irregular^lme on the south between 40° to 45° N.E., reaching as high as 75° to 

 80° N.E. Greenland and Newfoundland were portions of the same continent. 

 _ From the south-eastern extremity of this great continent there was an exten- 

 sion of the land south-west along the present Atlantic sea-hoard, much as 

 Tenasserim and Malacca stretch away at present from the East- Asian continent. 



On the European side the extent of land-surface was much less ; it included only 

 the Scandinavian mass, together with the greater portion of the British-Islands 

 group, the whole having a common strike from north-east to south-west ; but this 

 land had a much greater extension on the Atlantic side than at present ; and it 

 is very probahle, on other considerations, that at that time this old part of our 

 present European land-surface was one with that of th« American, the whole 

 tornimg a great circumpolar continent, ranging across more than 180° of longitude. 



The positions of certain insular masses, such as the central plateau of France and 

 others, were indicated. 



These geographical features of " Devonian " times were represented on a man of 

 the northern hemisphere. 



..ii°3®?i*'^,°i *¥ P'^rsistency with which the notion of the marine origin of the 

 Old Red Sandstone " of the British Islands, and its equivalency to the true 

 Devonian group, has been maintained by a few geologists, contrary opinions 

 have very generally gained ground, both at "home and ahroad. The evidence in 

 this direction has been greatly strengthened, both geologically and zoologically :— 

 l<irst, the Old Red Sandstone on the north side of the Bristol Channel is for the 

 most part distinguishable only by its external characters ; viewed in this way the 

 red sandstones and conglomerates of the Foreland, of Countesbury. and the hills 

 about Porlock (^orth Somerset) seem to be identically the same with the "Old 

 Red of South Monmouthshire, whilst they are wholly unlike, and indicate a very 

 ditierent ongm from the sandstones of the Linton group, which are true fossiliferous 

 marine Lower "Devonian." If this identification of the Foreland series, and of 

 Countesbury, be correct, then stratigraphically the lacustrine Old Red Sandstone 

 passes as a mass beneath the Devonian (Valley of the Lynn) 



,e 



