TKOPIDOLEPTUS FAUNA IN MARYLAND CHEMUNG 679 



RECURRENCE OF THE TR0PID0LEPTU8 FAUNA IN THE CHEMUNG OF 



MARYLAND^ 



BY CHARLES K. SWARTZ 



Contents Page 



Recurrence of faunas 679 



Historical review 679 



Lithological sequence 680 



Sections east of Wills mountain . . 682 



Section 1 % miles south of Round, West Virginia 682 



Section west of Okonoko 682 



Section west of Pawpaw 682 



More easterly sections 683 



Sections west of Wills mountain 683 



Section near Allegany grove 683 



Section near Ellersly 683 



Correlation of the various sections 684 



Correlation with the Upper Devonian of New York 685 



Geographical range of the genera Dalmanella and Douvillina in Maryland 685 



Conclusions 686 



Recurrence of Faunas 



The occurrence of a fauna characteristic of one geological formation within 

 the limits of another formation is a phenomenon of much interest, since it 

 affects the problem of the correlation of geological horizons. 



Barrande first clearly pointed out the possibly of the occurrence of one fauna 

 in the midst of another in his now famous doctrine of colonies. While his inter- 

 pretation of the sections studied by him has proved erroneous, the principle 

 enunciated has been of great importance, especially in suggesting the concep- 

 tion of the simultaneous existence of independent faunas in different areas. 

 Williams 2 subsequently applied the same principle to the Upper Devonian 

 strata of New York, and his work has been extended by many other students 

 of the problem. 



Four recurrences of the Hamilton fauna, termed by Williams the Tropidolep- 

 tus carinatus fauna, are recorded by him in the Upper Devonian strata of New 

 York above the summit of the Hamilton formation. 3 The uppermost of these 

 horizons lies within the Chemung of that state. 



The existence of similar recurrent faunas in the Chemung of Maryland has 

 recently been observed by the author, and he believes that the facts observed 

 and certain conclusions based upon them, may be worthy of communication. A 

 brief historical statement will be helpful in understanding the discussion. 



Historical Review 



The Upper Devonian of Maryland presents two well defined facies, a lower 

 marine division and an upper division having the characteristics of the Catskill 

 of New York. 



1 Published by permission of the Director of the Maryland Geological Survey. Manu- 

 script received by the Secretary of the Society June 5, 1909. 



2 Proceedings of the American Association for the Advancement of Science, vol. xxx, 

 1881, p. 186. U. S. Geological Survey, Bull. no. 3, 1884. 



3 Journal of Geology, vol. xv, 1907, pp. 108-110. 



