ANNIVERSARY ADDRESS OF THE PRESIDENT. Cxlvil 



unfossiliferous ; but it is followed by fossiliferous schists and lime- 

 stones. The Oscarskal group is composed of calcareous and argil- 

 laceous rocks, including Encrinital schists. The Malmo group is 

 argillaceous at its base, with calcareous flags and a Pentamerus- 

 limestone, an upper Orthoceratite-limestone, and an upper Grap- 

 tolite- schist, — repetitions which strongly prove that they are but 

 the natural alternations of mineral deposits, accompanied by a cor- 

 responding variation in the organic structures which belong to any 

 one great geological formation. The total thickness of the fossili- 

 ferous rocks is above 1900 feet; and Sir Roderick classes the lower 

 and the upper Oslo and the Oscarskal series, or the lower eight 

 subdivisions, with the Lower Silurian as representing the Stiper- 

 stones, the Llandeilo, and the Caradoc series, and the lower and upper 

 Malmo, or the six upper subdivisions, with^the Upper Silurian as 

 representing the Llandovery, the Ludlow, and the Wenlock series. 



In the comparison of the fossils of the Silurian basin of Christiania 

 with those of Great Britain, Sir Roderick has of course found many 

 specific differences; but the coincidence in the succession of the fossils, 

 considering the distance between the localities, is stated to be truly 

 remarkable, and without doubt it is by this correspondence in the 

 change of organic life in two different and distant regions that their 

 identity as formations must be determined, rather than by an actual 

 identity of species, which ought not to be expected under such cir- 

 cumstances. Occasionally, however, common species step in to decide 

 on the true value of a bed ; and thus the alum-slates of Norway, which 

 from its Trilobites had been supposed to belong to a peculiar zone, 

 are by OrtJiis calligramma and Didymograpsas geminns brought 

 into direct connexion with unquestionable British Lower Silurian 

 deposits, such as the Stiper-stones and Longmynd rocks. Taking 

 indeed the whole thickness of the Scandinavian beds with all their 

 subdivisions, Sir Roderick maintains that, though so much less ex- 

 tended in development than the British, it constitutes one conform- 

 able and natural system, whether viewed physically or zoologically. 

 "Where pierced by eruptive rocks, some of the members of the Silu- 

 rian series have been metamorphosed into crystal line gneiss- — a fact 

 which has been confirmed by Mr. David Forbes. 



The Silurian deposits of Esthonia and Livonia, as described by 

 M. Schmidt, differ in physical character from those of Norway, 

 as calcareous bands constitute the greater portion of them. M. 

 Schmidt recognizes five stages, each of which is characterized 

 by a peculiar fauna, — very few species traversing two entire 

 stages, some being present in the two upper, and some in the 

 two lower, whereas only one species, the Calymene Blumenbachii, 

 passes through the five lower stages, being, however, in the fifth, 

 the equivalent of the Upper Ludlow, modified into G. spectabilis of 

 Angehn. The sharpest separation is between the second and third 

 bands, or between the Lower and Upper Silurian, though there is 

 even there a sufficient transition to show that there has been no 

 " violent break in the development of organic life," or such as could 

 warrant the separation of the lower from the upper Silurian as part 



