1865.] DAWSON— COAL-FOEMATION. 141 



cliaracteristic of BigiUaria, Calamodendron, and Dadoxylon. In the 

 two former genera the disks or pores are large and irregularly ar- 

 ranged, either in one row or several rows. In the latter case they 

 are sometimes regularly alternate and contiguous. In the genus 

 Dadoxylon they are of smaller size and always regularly contiguous 

 in two or more rows, so as to present an hexagonal areolation. Dis- 

 cigerous structures of /Sigillaria and Ccdamodendron are very abun- 

 dant in the coal, and numerous examples were figured in my former 

 paper. I have indicated by the name lleticidated Tissue certain 

 cells or vessels which may either be reticulated scalariform vessels, 

 or an imperfect form of discigerous tissue. I believe them to belong- 

 to Stigmaria or Ccdamodendron. (Figs. 57 & 68, PI. XII.) 



e. 'kpideronal tissue. — This is a dense cellular tissue representing 

 the outer integuments of various leaves, herbaceous stems, and fruits. 

 I have ascertained that the structures in question occur in the leaves 

 and stipes of Cordaites and ferns, and in the outer coat of Carpolites 

 and Sporangites. With this I may include the obscure and thick- 

 walled cellular tissue of the outer bark of Sigillaria and Lepidoden- 

 dron and other trees, which, though usually consolidated into com- 

 pact coal, sometimes exhibits its structure. 



I would here emphatically state that all my observations at the 

 Joggins confirm the conclusion, which I arrived at many years ago 

 from the study of the coals of Pictou and Sydney, that the layers 

 of clear shining coal (pitch or cherry coal) are composed of flattened 

 trunks of trees, and that of these usually the bark alone remains ; 

 further that the lamination of the coal is due to the superposition of 

 layers of such flattened trunks alternating with the accumidations of 

 vegetable matter of successive years, and occasionally with fine vege- 

 table muck or mud spread over the surface by rains or by inundations. 

 In connexion with this, it is to be observed that the density and im- 

 permeability of cortical tissues not only enable them to endure after 

 wood has perished or been resolved into bits of charcoal, but render 

 them less liable than the wood to mineral infiltration. 



14. Bate of Groivth of Carboniferous Plants. — Yery vague state- 

 ments are often made as to the supposed rapid rate of growth of plants 

 in the Carboniferous period. Perhaps the most trustworthy facts in 

 relation to this subject are those which may be obtained from the 

 coniferous trees. In some of these (for instance, Dadoxylon materi- 

 arium, D. annulatum, and D. antiqidus) the rings of growth, which 

 were no doubt annual, are distinctly marked. On measuring these 

 in a number of specimens, and comparing them with modern species, 

 I find that they are about equal in dimensions to those of the 

 Balsam-Fir or the Yellow Pine of America. Assuming, there- 

 fore, similarity in habit of growth and extent of foliage to these 

 species, we may infer that, in regard to coniferous trees, the 

 ordinary conditions of growth were not dissimilar from those of 

 Eastern America in its temperate regions at present. When, how- 

 ever, we compare the ferns and Zycojwdiacece of the Coal- formation 

 with those now growing in Eastern America, we see, in the much 

 greater dimensions and luxuriance of the former, evidence of a much 



