AMERICAN GEOLOGY DECADE OF 1850-1859. 



U7 



aquatic circumstances, which were not accompanied by any material 

 permanent change in the nature of the surface of the land and its 

 organized inhabitants. He conceived that the elevation and depression 

 of large areas were not absolutely contemporaneous, but such that by 

 a mere change of place one could have passed from a coal swamp to a 

 modiola lagoon or a tidal sand Hat. 



In the Quarterly Journal of the Geological Society for 1859 Daw- 

 son had another important paper on the vegetable - structures in the 

 coal in which he announced that the vegetable matter of these beds 

 consists principally of Sigillaria? and Calamitea?. With these, how- 

 ever, he found intermixed remains of many other plants. 



The structure of the coal as he here found it conformed to the view 

 that the materials were accumulated by growth in place without any 

 driftage of materials. The rate of accumulation he thought to have 

 been very slow, the climate of the period being such that the true coni- 

 fers grew not more rapidly than their modern congeners. Making all 

 due allowances, he felt safe in asserting that every foot of thickness of 

 pure bituminous coal implied the growth and fall of at least fifty gen- 

 erations of Sigillaria? and, therefore, an undisturbed condition of forest 

 growth enduring through many centuries. 



In this same journal for 1865, under the title of On the Conditions 

 of the Deposition of Coal, he again referred to the subject. Writing 

 with reference only to the beds of Nova Scotia and New Brunswick 

 and their associated sediments, he showed that the coarser matter of 

 the Carboniferous rocks was derived from the neighboring metamor- 

 phic ridges, but much of the finer material was probably drifted from 

 more distant sources. He thought there was no good reason to doubt 

 that in the Carboniferous period the greater part of the Laurentian 

 and Silurian districts of North America existed as land. Considering 

 the relative position and lithological nature of the beds of the Car- 

 boniferous period, and comparing them with those of other periods of 

 the Paleozoic age in eastern America, he thought to find indications of 

 the existence of periodic cycles such that similar beds were deposited at 

 corresponding periods in each, the parallelism being tabulated as below: 



(The several formations are arranged in descending order.) 



Character of group. 



shallow, subsiding marine 

 area, tilling up with sedi- 

 ment. 



Elevation, followed by slow 

 subsidence, land, sur- 

 faces, etc. 



Marine conditions; forma- 

 tion of limestones, etc. 



Subsidence; disturbances; 

 deposition of coarse sedi- 

 ment. 



Lower Silurian. 



Upper Silurian. 



Devonian. 



Carboniferous 



Hudson River Lower Helder- Chemung group . 

 group. berg group. 



Upper coal for- 

 mation. 



Ptiea shale Salina group . . 



Trenton, Black Niagara and 



River, and | Clinton litne- 



Chazy lime- | stones, 

 stones. 



Potsdam and I Oneida and Me- 

 Calciferous ; dina sand- 

 sandstones, stones. 



Hamilton group..! Coal Measures. 



Corniferous limi 



stone. 



( iriskany 

 stone. 



bowel' Carbon 



i fen his lime- 

 stone. 



Lower Coal 

 Measures and 



conglomerate. 



