574 Wm. F. Prouty — Meso-Silurian Deposits of Maryland. 



sented in Maryland. That there were short periods, however, 

 when the low barrier separating this Cumberland Gulf from 

 the interior epicontinental sea was ineffective, is shown by a 

 few zones in the Maryland Meso-Silurian which have a prolific 

 development of certain of the more important Western New 

 York forms, as for instance the Dalmanites limulurus zone, 

 the Nucleospira pisiformis zone and the Camarotoechia obtu- 

 siplicata zone. (See fig. 3.) 



The great coral development of the western upper Niagara 

 is entirely lacking in the Maryland deposits. In fact there 

 are practically no fossils which belong distinctively to the 

 Lockport or Guelph formation, and it is probable that during 

 the greater part of these two periods there was little or no 

 sedimentation in the Maryland area. The Meso-Silurian sea 

 may have continued to exist in the Cumberland Gulf in early 

 Lockport time, but if so, seemingly for a short period only. 



It is further interesting to note that one fourth of all the 

 previously described forms are of world-wide distribution; 

 that six of the old forms are characteristic of the deposits of 

 Anticosti, Arisaig or the English Silurian, while fourteen are 

 characteristic of the western interior. This last result is, how- 

 ever, of little value in showing the relative ease of communica- 

 tion between the Cumberland basin and the epicontinental sea 

 to the west and the Canadian deposits to the north and east, 

 since the Canadian deposits have not been studied as well as 

 have those of the interior United States. 



Summary. 



The Meso-Silurian deposits of Maryland, lying between the 

 Tuscarora and the Salina formation, are about 800 7 in thickness 

 and are composed for the most part of shales and thin-bedded 

 sandstones below and of shales and limestone above. This 

 series can be divided into two formations, corresponding in 

 time approximately to the Clinton, accorded to the common 

 usage, and the Rochester of New York. They are, moreover, 

 taken together, the probable equivalent of Hall's typical Clin- 

 ton as represented at Clinton, Oneida Co., N. Y. 



These Meso-Silurian rocks outcrop in the western part of 

 Maryland in Allegany and "Washington Counties in six anticlinal 

 folds with typical Appalachian structure. The thickening of 

 the coarser sediments from the western to the eastern exposures 

 indicate the proximity of a shore line toward the east. That a 

 shore line or barrier existed not far to the west of the exposed 

 Maryland Meso-Silurian deposits is not evidenced by a lithogi- 

 cal study, but is sufficiently indicated by the fossil study. This 

 barrier must, however, have been low and at periods ineffective, 

 especially during Rochester time, when, to a greater extent 

 than in the Clinton, well marked fossil zones appear, making 

 a prolific development of some of the more important species 

 of western New York. 



