6S HISTORICAL PALyEONTOLOGY. 



tons of marine animals. It would, in fact, be a matter of 

 great difficulty to account for the formation of these great cal- 

 careous masses on any other hypothesis. (3) The occurrence of 

 phosphate of lime in the Laurentian Rocks in great abundance, 

 and sometimes in the form of irregular beds, may very possibly 

 be connected with the former existence in the strata of the re- 

 mains of marine animals of whose skeleton this mineral is a con- 

 stituent. (4) The Laurentian Rocks contain a vast amount of 

 carbon in the form of black-lead or graphite. This mineral is 

 especially abundant in the Hmestones, occurring in regular beds, 

 in veins or strings, or disseminated through the body of the lime- 

 stone in the shape of crystals, scales, or irregular masses. The 

 amount of graphite in some parts of the Lower Laurentian is 

 so great that it has been calculated as equal to the quantity of 

 carbon present in an equal thickness of the Coal-measures. 

 The general source of solid carbon in the crust of the earth 

 is, however, plant-life ; and it seems impossible to account for 

 the Laurentian graphite, except upon the supposition that it 

 is metamorphosed vegetable matter. (5) Lastly, the great 

 beds of iron-ore (peroxide and magnetic oxide) which occur 

 in the Laurentian series interstratified with the other rocks, 

 point with great probability to the action of vegetable life; 

 since similar deposits in later formations can commonly be 

 shown to have been formed by the deoxidising power of vege- 

 table matter in a state of decay. 



In the words of Principal Dawson, " any one of these rea- 

 sons might, in itself, be held insufficient to prove so great and, 

 at first sight, unlikely a conclusion as that of the existence of 

 abundant animal and vegetable life in the Laurentian ; but the 

 concurrence of the whole in a series of deposits unquestion- 

 ably marine, forms a chain of evidence so powerful that it 

 might command belief even if no fragment of any organic or 

 living form or structure had ever been recognised in these an- 

 cient rocks." Of late years, however, there have been dis- 

 covered in the Laurentian Rocks certain bodies which are 

 believed to be truly the remains of animals, and of which by 

 far the most important is the structure known under the now 

 celebrated name of Eozoon. If truly organic, a very special 

 and exceptional interest attaches itself to Eozoon, as being the 

 most ancient fossil animal of which we have any knowledge; 

 but there are some who regard it really a peculiar form of 

 mineral structure, and a severe, protracted, and still unfinished 

 controversy has been carried on as to its nature. Into this 

 controversy it is wholly unnecessary to enter here ; and it will 

 be sufficient to briefly explain the structure of Eozoon, as eluci- 

 dated by the elaborate and masterly investigations of Car- 



