144 WHAT MAY BE LEARNED FROM EOZOON 



matter. In evidence of this we sometimes find in a single canal 

 an outer tubular layer of serpentine and an inner filling of 

 dolomite, just as vessels of fossil plants are sometimes filled 

 with successive coats of different materials. In some well 

 preserved specimens we find the original cell wall represented 

 by a delicate white film, which under the microscope shows 

 minute needle-like parallel processes representing its still finer 

 tubuli. It is evident that to have filled these tubuli, the ser- 

 pentine must have been introduced in a state of actual solution, 

 and must have carried with it no foreign impurities. Conse 

 quently we find that in the chambers themselves the serpentine 

 is pure ; and if we examine it under polarized light, we see that 

 it presents a singularly curdled or irregularly laminated appear- 

 ance, as if it had an imperfectly crystalline structure, and had 

 been deposited in irregular laminse, beginning at the sides of 

 the chambers, and filling them toward the middle, and had 

 afterward been cracked by shrinkage, and the cracks filled with 

 a second deposit of serpentine.^ Now, serpentine is a hydrous 

 silicate of magnesia, and all that we need to suppose is that in 

 the waters of the Laurentian sea magnesia was present instead 

 of iron, alumina or potash, and we can understand that the 

 Laurentian fossil has been petrified by infiltration with ser- 

 pentine, as more modern Foraminifera have been with glaucon- 

 ite, which, though it does not contain magnesia, often has a 

 considerable percentage of alumina. Further, in specimens of 

 Eozoon from Burgess, the filling mineral is loganite, a com- 

 pound of silica, alumina, magnesia and iron with water, while 

 in other specimens the filling mineral is pyroxene. In like 



^ The same structures may be well seen in thin slices polished, to be 

 viewed as transparent objects, I may, however, explain that if these are 

 made roughly, and heated in the process, they may often show only 

 mineral structures and cleavage planes, whereas, if polished with great care 

 and slowly, and afterwards cleaned with an acid, they may show the 

 canals in great perfection. 



