216 



MINERALS AND GEOLOGY 



free ends of which form a kind of coronal on the top of the nucule. 

 These little bodies, when first found as fossils, were taken for foram- 

 inifera and called " gyrogonites." They occur in Triassic and many 

 higher (especially Cainozoic) fresh-water deposits. 



Vascular acrogens comprise the more typical acrogenous forms, 

 those in which vascular tissue is present. They include : Equisetacece, 

 Ferns and Opkioglossacece, Hydropteridce or Rhizocarps, Lycopodiacece, 

 and Lepidodendracece. The latter are usually placed with the lyco- 

 podiaceae, but although more or less closely allied to these, their true 

 affinities are still uncertain ; and their comparatively large size and 

 other characters warrant their separation as a distinct and higher 

 group. All are extinct ; and their remains are apparently confined 

 to Palaeozoic strata. 



The Equisetacece comprise only one living genus, Equisetum, com- 

 mon species of which are familiarly known as " Dutch rushes," 

 horsetails, &c. The Equiseti form hollow-jointed stems, arising from 

 creeping rhizomes or root-stalks, with, in fertile examples, a terminal 

 cone or spike containing the sporangia. The stem in most cases is 

 longitudinally striated, and the joints (in which, more especially, 

 silica is deposited) are surrounded by a toothed sheath of united 



FIG. 119. 

 Calamites inornatus (Dawson). Portage -chemung Formation. 



leaves or scales, and also in some examples by a whorl of slender 

 branchlets. Fossil forms are chiefly represented by Calamites, 

 although undoubted equiseti are known in carboniferous and higher 

 strata. Calamites are abundant in many Devonian and Carboniferous 

 beds. They occur usually in the form of stem-fragments (or impres- 

 sions of these), transversely jointed and longitudinally furrowed, and 

 as a rule more or less flattened or compressed. These stems vary 

 from about an inch, or less, to more than a foot in diameter, the 

 average width being from two or three to about six inches. Fig. 

 119 represents an example of a calamite from the dark bituminous 

 shales (Devonian) of Cape Ipperwash or Kettle Point in the town- 





