464 Notices of Memoirs — Address by Professor Peach. 



led to the accumulation of a great succession of calcareous deposits, 

 including the Beekmantown Limestone, to which reference has already- 

 been made. Schuchert, as already stated, has pointed out that, in the 

 lower part of the Ozarkic (Upper Cambrian) System, in Minnesota and 

 Wisconsin, the Gasteropod genera Holopea, Ophileta, and Rap}iistn)na 

 are associated with two sjiecies of Bikelocephalus. This nioUuscan fauna 

 is evidently the precursor of that of the Beekmantown Limestone. It 

 was probably from this central region of America that the calcareous 

 fauna of Beekmantown migrated to the submarine trough in the typical 

 Champlain region, and through Newfoundland to the North-West High- 

 lands of Scotland. 



The section at St. John, New Brunswick, where the Baltic and Welsh 

 types of the Oleiius fauna occur, shows that the southern shore-lino 

 of the trough must then have occupied much the same relative position 

 as in Lower and Middle Cambrian time. In the same region the 

 strata containing this fauna, with Peltura scarahcBoidea and Dictyonema 

 flabelliforme, are overlain by dark shales with Arenig Graptolites. 

 These Graptolite-bearing terrigenous deposits eventually extended across 

 the trough northwards, till, in Newfoundland, they came to rest on the 

 Beekmantown limestones. 



In the Lake Champlain region, in the Chazy Limestone, which there 

 immediately succeeds the Beekmantown Limestone without the inter- 

 vention of the Arenig Graptolite shale, there is a survival of the 

 Beekmantown molluscan fauna with only such slight modifications as t > 

 indicate genetic descent. In the same trough the descendants of thi^ 

 fauna are to be found in the Trenton Limestone. 



In this connexion it is worthy of note that the molluscan fauna an^ 

 the corals of tha Stinchar and Craighead Limestones of Upper Llandeilo age 

 in the Girvan district of the Southern Uplands have an American facies, 

 as first suggested by Nicholson. The appearance of American types in 

 these limestones may be accounted for in the following manner : 

 Attention has already been called to the divergent types of sedimentation 

 presented by the Upper Cambrian strata of the North-West Highland? 

 and of the South-East Highlands, at Stonehaven and Aberfoyle. In 

 the former case there is a continuous sequence of dolomites and lime- 

 stones, while in the latter we find a group, comprising Eadiolarian cherts 

 and black shales, associated with pillowy spilitic lavas and intrusive 

 igneous rocks, indicating conditions of deposition at or near the limit 

 of sedimentation. But, notwithstanding the different types of sedi- 

 mentation and the divergent faunas in the two areas, I believe that 

 during the Upper Cambrian period, and probably for some time there- 

 after, continuous sea extended from the North-West Highlands to beyond 

 the Eastern Highland border. The Upper Cambrian terrigenous sediments 

 which we now find at Stonehaven and Aberfoyle must have been derived 

 from land to the south. In Llandeilo time the Arenig and Lower 

 Llandeilo rocks of the Girvan area were elevated and subjected to 

 extensive denudation. On this highly eroded platform, as first proved 

 by Professor Lapworth, coarse conglomerates, composed of the under- 

 lying materials, were laid down in association with the Stinchar and 

 Craighead Limestones. In iny oiiinion the appearance of the American 

 forms in these limestones is connected with tlie movement that produced 

 this unconformability in the Girvan area. This local elevation wai 

 probably associated in some form with the great crustal movements that 

 culminated in the overthrusts of the North-West Highlands and caused 

 the intense folding and flaser structure of the rocks along the Highland 

 border. By these movements shore-lines may have been established 

 between the north side of the old Palajozoic sea and the Girvan area, 

 which permitted the southern migration of the American forms. 



Note. Since writing the above my attention has been directed to the 

 recent work of Bassler on The Early PalcBOzoic Bryozoa of the Baltic- 



