202 Mr. C. Lapwortli on the Geological 



is the M. colonus (of authors), which is peculiar, as also are 

 M. Boemeri } Ban*., M. scanicus, Tullberg, and many others. 

 This zone is magnificently developed in Britain and in the 

 south of Sweden, and is recognizable in Norway, Bohemia, 

 Bretagne, and the south of France. 



It is not pretended that each of the so-called zones enume- 

 rated above is of equal geological importance. The zones of 

 Tetragra/ptU8 (2), Didymograptus geminus (4), Coenograptus 

 gracilis (5), Monograptus gregarius (12), and Monograptus 

 Nilssoni (20) are of such paramount consequence, whether we 

 consider the thickness of their included strata in Britain, or 

 the great variety and wide geographical range of their dis- 

 tinctive faunas, that they deserve rather the titles of sub- 

 formations. On the other hand, two or three zones, notably 

 those of Dvplograptus vesiculosus (11) and Cyrtograptus 

 Linnarssoni (18), must, in the present state of our know- 

 ledge, be regarded merely as provisional stages, distinguished 

 locally by a few peculiar forms, as yet restricted in their 

 horizontal distribution. Again, the species which gives its 

 name to the zone has, in one or two instances, been detected 

 in the overlying bands, as is the case with Monograptus gre- 

 gariu8j Lapw., and more doubtfully with M. spinigerns, 

 Nich. ; but in these exceptional cases the species, instead of 

 being predominant in these overlying beds, is rare and incon- 

 spicuous. But, if we have correctly interpreted the materials 

 in our hands, it is indubitable that each of these zones marks 

 a special substage or horizon in the ascending series of the 

 Lower Palaeozoic rocks. The formation to which it most 

 naturally belongs is determined by the special facies of its 

 collective Graptolite fauna ; and its vertical place within that 

 formation is fixed by its peculiar and predominant species. 



This list must be regarded merely as a first attempt to de- 

 fine and localize the minor Graptolite faunas of these ancient 

 sediments, and to make them available for the proposes of the 

 geologist and zoologist, as indices of the systematic place of 

 their containing beds, or as evidences of the mode and direc- 

 tion of the development of life. It may confidently be ex- 

 pected that future research will soon fix more definitely the 

 composition and limits of the characteristic faunas of the 

 zones already recognized, extending the range of some of 

 their forms into neighbouring stages, detecting fresh criteria 

 in their separation, and adding largely to the number of the 

 zones themselves. 



The acceptance of our conclusion that the Graptolites are 

 as restricted in their vertical range as other and more per- 

 fectly and generally studied groups of fossils, is merely a 



