. 393 



whole outcrop may reveal definite assemblages in a definite 

 sequence. 



"The general appearance of the fine shale bands alterna- 

 ting Avith the sandstones, is that of a deltaic deposit, proba- 

 bly at the mouth of a great river or at its entry into a lake 

 or it might be, the bend of a lagoon (the remarkable lack 

 of marine fossils in the neighbourhood renders some such 

 view very probable) . The deposits appear to have collected 

 rapidly (geologically speaking). The difi"erence in the 

 species of the plants brought down from time to time in 

 the current of the river can be readily accounted for by 

 slight changes in the course of the water, or by flood effects 

 in different parts of its course. The Fern Ledges flora is 

 the remains of the inland flora of the period, and one 

 which had travelled down stream as debris for some 

 distance before being entombed. It is, therefore, natural 

 that sometimes one, and sometimes another species should 

 preponderate in the various beds now appearing in con- 

 secutive order; but the sequence of these plant remains 

 depended on local, fortuitous accidents, and do not appear 

 to be an indication of appreciable differences of geological 

 time." 



The plants in this series of beds are found in two forms. 

 (i) Scattered, isolated and infrequent trunks or branches, 

 some of Calamites, but mostly of branches of gymnospermic 

 wood of an ancient type generally known as Dadoxylon. 

 These occur principally in the sandstones alternating 

 with the shale bands. (2) The impressions of ferns, 

 Cordaites, Calamites, and other plants, forming the debris 

 of a rich, mixed flora, preserved in the series of shale 

 bands. It is unfortunate that these impressions are all 

 much altered. They often occur on slickensided surfaces, 

 and locally the shales have quite a slaty cleavage. The 

 plant impressions have been completely graphitized and 

 most of them consist merely of a bright film or streak on 

 the rock. 



"Though over 80 ''species" have been from time to 

 time described from the Fern Ledges flora, among all 

 these only about 40 are of value and have been determined 

 on a sufficiently sound basis to make them of any real 

 use in the comparison of this flora with others." In the 

 following list are given only such species as are thought 

 to have been determined from material that by competent 

 palseobotanists would be universally considered to be 



