THE LAURENTIAN ROCKS. 33 



of cellular plants, as, for example, mosses and lichens ; and if 

 so, there would be comparatively little hope of the distinct 

 preservation of their forms or tissues, or of our being able 

 to distinguish the remains of land-plants from those of Algae. 

 "We may sum up these facts and considerations in the 

 following statements : First, that somewhat obscure traces of 

 organic structure can be detected in the Laurentian graphite ; 

 secondly, that the general arrangement and microscopic struc- 

 ture of the substance corresponds with that of the carbon- 

 aceous and bituminous matters in marine formations of more 

 modern date ; thirdly, that if the Laurentian graphite has 

 been derived from vegetable matter, it has only undergone a 

 metamorphosis similar in kind to that which organic matter 

 in metamorphosed sediment of later age has experienced; 

 fourthly, that the association of the graphitic matter with 

 organic limestone, beds of iron ore, and metallic sulphides, 

 greatly strengthens the probability of its vegetable origin ; 

 fifthly, that when we consider the immense thickness and 

 extent of the Eozoonal and graphitic limestones and iron ore 

 deposits of the Laurentian, if we admit the organic origin of 

 the limestone and graphite, we must be prepared to believe 

 that the life of that early period, though it may have ex- 

 isted under low forms, was most copiously developed, and 

 that it equalled, perhaps surpassed, in its results, in the way 

 of geological accumulation, that of any subsequent period." 



(D.) WESTERN AND OTHER LAURENTIAN EOCKS, ETC. 



In the map of the Laurentian nucleus of America (fig. 4,) 

 I have not inserted the Laurentian rocks believed to exist in 

 the Eocky Mountains and other western ranges. Their dis- 

 tribution is at present uncertain, as well as the date of their 

 elevation. They may indicate an old line of Laurentian 

 fracture or wrinkling, parallel to the west coast, and defining 

 its direction. In the map there should be a patch of Lauren- 

 tian in the north of Newfoundland, and it should be wider at 

 the west end of lake Superior. 



Full details as to the Laurentian rocks of Canada and sec- 



D 



