THE MEDINA SERIES 535 



always occurs on the under surface of the sandstone lying upon a shale 

 bed. The bedding is very regular and more or less cross-bedding is 

 usually present; channeling is a rare feature in the lower part of the 

 formation. Ripple-markings are also present, though not common. Sun- 

 cracking occurs rarely and only near the top of the Shawangunk, and 

 rain-prints were not seen by the writer. Intraformational shale con- 

 glomerates are at times well developed near the upper or lower limits of 

 a sandstone and signify the local disrupting of a thin shale bed by the 

 storm-generated waves in this shallow-water deposit. Grains and small 

 nodules of siderite are usually abundant and when weathered give the 

 sandstones a spotted appearance. In the lower third of the Shawangunk 

 there is also usually present some feldspar, along with small fragments 

 of serpentine. To the writer all this evidence is in favor of the view 

 that the deposits are of the shallow sea and near the shore — great shallow- 

 water flats of moving sands in which lived, now here and now there, in 

 great abundance, an errant annelid, ArtJirophycus alleglianiense, similar 

 to the lob-worms of the English sand beaches. On the mud bottoms the 

 eurypterids were often present in great numbers and in variety of form ; 

 usually the younger growth stages are most prevalent, though large indi- 

 viduals are represented by fragments. To Clarke and Euedemann "the 

 Shawangunk grit represents ;i tidal zone deposit of an encroaching sea 

 or of a delta." 12 



These sands and conglomerates came from Appalachia to the east of 

 the present Atlantic shoreline, then a high land of crystalline rocks ele- 

 vated in late Ordovician time during the Taconic Disturbance. The 

 rivers were long and had reduced the quartz to fine sand and fairly well- 

 rounded, small pebbles, and the work of the sea waves had washed into 

 deep water the muds, of which so little comparatively is present in the 

 Shawangunk and Tuscarora formations. On the other hand, Grabau 13 

 would have us believe with him that the Shawangunk is a subaerial or 

 torrential deposit formed entirely on dry land, and that in the rivers lived 

 the eurypterids ; their dead bodies were not only washed into these sands, 

 but were also carried out into the sea. Brown, 14 however, holds correctly 

 that "the fine-grained sandy character of this formation [Shawangunk] 

 throughout the greater part of its depth is hardly consistent with the 

 torrential theory of its origin." Its sediments "can not be interpreted as 

 subaerial deposits of the alluvial fan type, and there is no apparent 

 reason why they should be considered delta rather than normal shore 

 deposits." 



12 Op. cit, p. 105. 



"Bull. Geol. Soc. Am., vol. 24, 1913. 



"Op. cit, p. 474. 



