86 



The Canadian Field-Naturalist 



[Vol. XXXVI 



these occur also in the Trenton of Kentucky, and 

 the last ranges as far west as Minnesota. 



From the preceding notes it is evident that 

 during Trenton times the Ottawa echinoderm 

 fauna ranged as far east as Montreal, as far west 

 as Minnesota, and as far south as New York and 

 central Kentucky. 



In the Ottawa are, however, there are three 

 echinoderm horizons. Of these the lowest hori- 

 zon forms the lower third of the Hull member, 

 about 35 feet above the base of the Trenton 

 formation. The second horizon occurs 160 feet 

 above the base of the Trenton, a short distance 

 above the lower quarter of the Prasopora member, 

 which is regarded as corresponding best to the 

 typical Trenton of New York. The third zone 

 occurs about 235 feet above the base of the 

 Trenton, in the lower part of the Picton member. 

 Of these three horizons the lower and middle 

 ones are of special interest in this connection 

 because they contain the largest and most varied 

 of the echinoderm faunas. 



The lower or Hull horizon is stated by Prof. 

 Raymond (Bui. Mus. Comparative Zoology, vol. 

 56, No. 3, 1916, p. 260) to be well exposed at 

 Kirkfield, and to be very near the horizon of the 

 Curdsville member of the Trenton in central 

 Kentucky. The exposures in eastern New York 

 and at Montreal which contain Pleurocystites, and 

 which belong to the Glens Falls member at the 

 base of the Trenton, are regarded by him to be 

 probably of about the same age as the Hull beds. 



The middle or Prasopora horizon is that part 

 of the Trenton best exposed at Trenton Falls, the 

 type section of the Trenton in New York. It is 

 characterized by the presence of Clitambonites. 



The upper or Picton horizon is characterized by 

 the presence of Strophomena trilobita, Rafines- 

 quina delfoidea, and Cydospira bisulcata, and, 

 acccording to Prof. Raymond, probably is the 

 horizon with which the Minnesota cystid bed, in 

 the upper part of the Prosser formation, is to be 

 correlated. 



Apparently the Ottawa echinoderm fauna 

 extended farthest south and east during the 

 deposition of the lowest or Hull horizon. During 

 the deposition of the middle or Prasopora horizon 

 strata it apparently did not reach Montreal on 

 the east, nor extend far beyond north-central New 

 York in a southward direction. Possibly the 



exposures along the Escanaba River in northern 

 Michigan belong here. During the deposition of 

 the upper or Picton strata the Ottawa echinoderm 

 fauna apparently reached the Minnesota area. 

 Finally, during the deposition of the lower Ma- 

 quoketa there appears to have been a reinvasion 

 of the Ottawa Trenton echinoderm fauna from 

 some unknown northern area to which it had 

 retreated during the long period intervening 

 between the close of the Trenton and the beginning 

 of the Maquoketa. 



During early Trenton times southern Ontario, 

 including Ottawa and Kirkfield, appears to have 

 been a center of distribution from which the Ottawa 

 echinoderm fauna radiated in different directions. 



Fore-runners of this fauna appear already in the 

 Chazyan of southern Quebec, of the Lake Cham- 

 plain area of New York, and in various parts of 

 Tennessee. It remains to be determined from 

 what areas this echinoderm fauna invaded southern 

 Ontario in early Trenton times, but present 

 information suggests at least that later, during the 

 Trenton and subsequent to the Trenton, this 

 fauna was largely of northern distribution. 



A few of these genera are known also from Euro- 

 pean strata but these do not indicate the origin 

 of the Ottawa echinoderm fauna from European 

 sources. The presence of Cheirocrinus in Great 

 Britain and in the northwestern part of the 

 continent of Europe, including the Baltic pro- 

 vinces, is indicative rather of the northern dis- 

 tribution of this genus, since the Chazyan species 

 found in America appear to be as old as anything 

 found in Europe. In a similar manner, the 

 occurrence of Pleurocystites in Ireland, Wales, and 

 the Girvan district of Scotland, and the failure of 

 its appearance on the continent, suggests the 

 origin of the British species from American 

 sources, rather than the reverse, the American 

 species from the Ottawa area being regarded by 

 Dr. Bather as distinctly older (Trans. Royal Soc 

 Edinburgh, 49, pt. II, 1913, p. 460). 



It is not unlikely that the greater part of the 

 Ottawa echinoderm fauna is distinctly of American 

 origin, though the data are not yet at hand to 

 determine its sources. More detailed knowledge 

 of American Chazyan echinoderm faunas is 

 necessary to trace the origin of the Ottawa faunas 

 one step backward. 



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