680 PROCEEDINGS OF THE BALTIMORE MEETING 



The lower marine strata are known as the Jennings formation. This forma- 

 tion has long been recognized as equivalent, in a general way, to the Genesee, 

 Portage, and Chemung of New York. The Jennings of Maryland has been 

 studied by Professor C. S. Prosser, who has prepared a monographic treatment 

 of the subject to be issued in the forthcoming volume of the Maryland Geo- 

 logical Survey, upon the Devonian of Maryland. An extended and admirable 

 study of the fauna was made by Dr J. M. Clarke, of Albany, New York, whose 

 work will appear in the same volume. A brief summary of the results ob- 

 tained by these workers was published by Professor Prosser in the Journal of 

 Geology in 1901.* 



The author wishes to acknowledge his indebtedness to these two gentlemen, 

 with whose work he has been acquainted, in advance of its full publication, in 

 the prosecution of his own studies. A full statement of their results will ap- 

 pear in the volume mentioned. 



The author subsequently showed that a fauna similar to the Ithaca fauna of 

 New York occurs in the Portage of Maryland, and that this is succeeded by a 

 fauna of marked Hamilton type, frequently abounding in Tropidoleptus carin- 

 atus, which occurs in the Portage below the strata containing the typical Che- 

 mung species. 5 



At the time of the publication of the paper referred to, the occurrence of the 

 Tropidoleptus carinatus fauna above the base of the Chemung fauna had not 

 been observed by the writer and his associates. 6 



During the past summer Tropidoleptus carinatus and associated Hamilton 

 species have been observed about 600 feet above the base of the Chemung 

 fauna. It is to record this occurrence that the present communication is made. 

 The author wishes to acknowledge his great indebtedness to Professor D. W. 

 Ohern, to whom he is under obligations for constant and most intelligent co- 

 operation in the prosecution of this entire investigation, and to Dr T. P. May- 

 nard, who has assisted in measuring certain of the sections described. 



Before considering the fauna it will be helpful to discuss the lithological 

 sequence in the Upper Devonian of Maryland. 



Lithological Sequence 



The Jennings of Maryland embraces nearly 5,000 feet of strata. At the base, 

 in the west, are the black shales of the Genesee member. Above this succeed 

 argillaceous shales alternating with thin sandstones, the percentage of sand- 

 stone increasing in the upper part of this zone. These shales and interbedded 

 flaggy sandstones bear the Naples fauna as in New York. They are succeeded 

 by slightly more arenaceous sediments bearing a profuse development of the 

 Ithaca fauna characterized by the dominance of Spirifer penatus var. posterns 

 Hall and Clarke. Overlying the latter appear more arenaceous sediments con- 

 taining prominent conglomerates in the east and bearing a profuse fauna of 

 distinctly Hamilton type, dominated by the presence of Tropidoleptus carinatus 





* Journal of Geology, vol. ix, 1901, pp. 419-420. 



5 Journal of Geology, vol. xvi, 1908, p. 328. 



6 Professor Prosser had observed the occurrence of Tropidoleptus carinatus In his study 

 of the Jennings, but had not determined its horizon with respect to the succession of 

 faunas here discussed. 



