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orthoceratites upwards of 10 feet long. Their function appears 

 to liave been to keep the seas clear of superfluous animal matter. 

 No one who has looked a cuttle-fish in the face would wish 

 to cope with an enlarged addition of the uncanny creature, 

 however beautiful its shell might be. 



Having now described what we are to look for in past life, 

 I must briefly refer a little more fully to the places where we 

 are to make our search. , 



The lowest group of sedimentary rocks is called the 

 Laurentian, largely developed in Canada, where it was first 

 distinguished and named. This is estimated at 30,000 feet 

 thick, and consists of gneiss, quartz-rock, and limestone, 

 with occasional beds of graphite. The old granitic rocks of 

 the West of Scotland, and the hard, dark rocks of Skye, are 

 supposed to belong to this series. No trace of organic life 

 has been seen in any part of this vast formation, with the 

 single exception of the masses of eozoon, a foraminifer 

 developed and elucidated by the happy labours of Dr. 

 Dawson, of Montreal. Next to the Laurentian, lying upon it, 

 comes a series of coarse, hard rocks, called the Huronian, 

 in which no fossils have yet been found. The reason for 

 placing the Huronian over the Laurentian is that the former lies 

 unconformably on the upturned edges of the latter. Next in 

 the ascending scale is the series in which our best slates 

 are found in Wales, and hence called the Cambrian. These 

 show, in some of their layers, very numerous remains of small 

 marine animals, including a bivalve mollusc called Lingula. 

 The Lingula zone is the equivalent of the Potsdam sandstone 

 of North America, and of the primordial zone in Bohemia. 

 The Skiddaw slates in Cumberland, and the Quebec group 

 and calciferous slates of New York county are also on this 

 horizon. The assemblage of organic life shown by these rocks 

 displays the well-known curious crustaceans as called trilobites, 

 with great numbers of graptolites, and some shells and sea- 

 urchins but no cephalopods. Next in our upward course occurs 

 a series of slaty rocks, named, from the place where they were 

 first distinguished, the Tremadoc slates. These are on the 

 upper Cambrian level, and contain a distinct collection of 

 animated life, still marine only, and numbering, for the first 

 time, cephalopods. Amongst these latter the bent form, cyrto- 

 ceras, occurs in the lowest beds, and the straight form, the 

 orthoceras, over them, as may be seen, at Tremadoc, in North 

 Wales. 



Dr. Blake, the chronicler of the British cephalopods, 

 writes : — '' The first to appear is cyrtoceras, represented by 

 0. prcecox, though followed in the uppermost division of the 



VOL. XVIII. U 



