138 PROTOZOA. 



mode of occurrence of Eozobn, the chief structural features which it 

 presents in thin sections, and the general explanation of these features 

 given respectively by those who regard it as Foraminiferal and those who 

 consider it to be a purely mineral structure. In addition, it may not be 

 out of place to indicate a few considerations based upon a prolonged and 

 careful microscopical investigation which the present writer has inde- 

 pendently carried out into the structure of this problematical body. 



The peculiar structure which has been described under the name of 

 Eozobn Canadense occurs in the crystalline metamorphic limestones of 

 the Lower Laurentian in Canada, and it has also been detected in the 

 same country in similar limestones believed to be of the age of the Upper 

 Laurentian or Huronian. An allied form (species ?) has been found in 

 rocks supposed to be Laurentian in Newfoundland ; and Dr Gumbel has 

 described a third form from crystalline limestone belonging to the 

 " Hercynian gneiss formation" (Lower Cambrian or Huronian?) of 

 Bavaria. 



As regards its mode of occurrence, Eozobn appears to most com- 

 monly present itself in the form of spreading layers or confluent masses. 

 According to Sir William Dawson, however, comparatively small, isolated 

 specimens are found, which have a " broadly-turbinate, funnel-shaped, 

 or top-shaped form, sometimes with a depression on the upper surface." 

 The same observer has also described the occurrence of vertical tubes 

 of large size traversing masses of Eozobn, and has compared these with 

 the oscular canals of Sponges. 



As regards its macroscopic characters, a mass of Eozobn shows a con- 

 spicuous structure out of thin alternating laminae, arranged parallel with 

 one another and often more or less concentrically (fig. 40). The laminae 



Fig. 40. — Fragment of Eozodn, of the natural size, showing alternating laminae of loganite 

 and dolomite. (After Dawson.) 



of such a mass are usually of different colours and composition ; one 

 series being white, and composed of carbonate of lime — whilst the 

 laminae of the second series alternate with the preceding, are green in 

 colour, and are found by chemical analysis to consist of some silicate, 

 generally serpentine or the closely related " loganite," or white pyroxene. 

 In some instances, however, according to Dawson, all the laminae are 

 calcareous, the concentric arrangement still remaining visible in conse- 

 quence of the fact that the laminae are composed alternately of lighter 

 and darker coloured limestone. The calcareous layers (fig. 41, A) are 

 composed of coarsely crystalline calcite (as viewed macroscopically), and 



