AUSTEN ON THE BOULONNAIS. 245 



in a zone which extends from Plymouth to Newton, beneath the 

 great coral limestone group ; in North Devon they occur at the base 

 of the thick calcareous series, which comes out on the sea-coast, in 

 Combe Martin Bay ; they have a like position in the limestone band 

 of Givet. Calceola follows a like continuous and very narrow zone. 

 We are safe therefore in placing the Ilfracombe group as the equi- 

 valent of the coral limestones of Newton ; and in comparing both 

 with the calcareous groups of Givet, of theEifel, and ofVillmar, in spite 

 of the want of correspondence which they present in their mineral and 

 organic compositions, simply because there are peculiar forms which 

 occur but once in each series, and for a brief space only, when esti- 

 mated with reference to the dimensions of these groups, and that it 

 is not possible that these forms should range out of any beds, but 

 such as were in immediate extension of those in which they were first 

 introduced. Such zones become our only positive terms of com- 

 parison, and all that is required to render it complete is that the inter^ 

 mediate grouping should be in general harmony with the progressive 

 change which the whole of the series exhibits. The grouping which 

 such considerations suggest, is best exhibited in a tabular form ; but 

 there is one part of the upper Palaeozoic series which has long been of 

 interest to English geologists, and to which perhaps some have given 

 an undue importance. The Old Red Sandstone of the British series 

 is exhibited with such very characteristic features, over a large area, 

 that we must necessarily assign it a representative position ; but it 

 must be borne in mind that this group is only an indication of cer- 

 tain conditions of accumulation, though of considerable continuity. 

 Having seen the Old Red Sandstone in the counties of Hereford, 

 Pembroke, Monmouth, and Somerset, I may state that this portion, 

 which is its typical mass, belongs to the littoral, sublittoral, and 

 drift-sand zones, and that as such it can only be a subordinate group 

 in a perfect series of marine sedimentary deposits ; the distance, how- 

 ever, is not so great but that we might look for it in some approxi- 

 mately recognizable form in the south of theExmoor range, unless that 

 district had been raised out of the area of the sedimentary beds of that 

 period, a supposition which cannot be entertained. It must be re^ 

 membered, that for the area above referred to, the Old Red Sandstone 

 is a continuous group, which must always be the strongest proof of 

 identity of geological age. In Somerset as elsewhere the Old Red 

 Sandstone passes into the Lower Mountain Limestone, by a series of 

 beds which indicate a progressive increase of depth merely, but no 

 cessation. I am therefore unable to adopt the classification proposed 

 by Mr. Sharpe in a recent communication*, the result of our Belgian 

 excursion, as it would make the Old Red Sandstone older than the 

 calcareous group of South Devon. The changes which such beds as 

 those of the Old Red Sandstone may be expected to present else- 

 where, depend on the determination of the physical changes which 

 affected Western Europe anterior to and during the Anthraciferous 

 period ; these changes are indicated in the second part of this com- 

 mimication, and in accordance with these, I have neither looked for 

 typical Old Red Sandstone, nor Mountain Limestone, but simply for 

 representative conditions. 



* Quarterly Journal, vol. ix. p. 26. 



