FORAMINIFERA. 



139 



vary much in thickness, not only in different specimens, but commonly 

 in different parts of the same specimen. According to Dawson, in 

 isolated, inversely conical specimens it is the laminae at the base which 

 are the thickest. Very commonly, the laminae subdivide and coalesce 

 with one another. The serpentinous layers, which alternate with the 

 calcareous laminae, usually show a more or less conspicuous structure 









Fig. 41. — Minute structure of Eozoon Canadcnse, from the Laurentian limestones of Canada. 

 a, Part of a vertical section of Eozoon, enlarged about ten times, showing the alternating layers 

 of calcite (c) and serpentine (s) ; b, Part of a calcareous lamina, cut vertically, showing the 

 " canal-system," enlarged about forty-five times ; c, Part of a calcareous lamina, cut horizontally, 

 and enlarged about sixty times, showing the large and small branches of the canal-system ; d, 

 Part of a vertical section of a calcareous lamina, enlarged about one hundred times, showing the 

 finer divisions of the canal-system and the so-called "proper wall" («/). c, Calcareous laminae; 

 s, Serpentinous lamina? ; w, The so-called "proper wall " ; ca, Large branches of the canal-system. 

 (Original.) 



out of small rounded or lenticular masses. This characteristic botryoidal 

 structure of the serpentinous laminae is best studied in polished specimens 

 which have been treated with weak acids, so as to dissolve out the cal- 

 careous portions of the mass to a limited depth below the surface. 



As regards the microscopic structure of Eozoon, the calcareous laminae, 

 in well-preserved examples, exhibit a very remarkable canaliculated or 



