SUMMARY OF EARLY SIIAJRIC DEPOSITS 489 



Medina are both unconformable to the underlying Hudson beds. Since 

 we know that the older strata in the east were folded at the end of Ordo- 

 vicic time, we seem to have here indication that this folding was also in 

 pre-Medina time. 



If we conceive of a series of strong folds formed along the eastern area 

 of the Appalachian region at the end of Ordovicic time, the surface rock 

 of such folds would be the red Juniata-Bays, while beneath would be the 

 white or gray Balcl Eagle, also involved in the folds, but at first out of 

 sight. Erosion, which would set in at once, would thus attack the "red" v: 

 rocks first and so furnish oxidized sands and muds which are spread by 

 the rivers over the surfaces west of the folds, an area which had not been 

 included in the folding. Thus red sands and muds of Siluric age derived 

 from the folded, red Ordovicic rocks would come to rest on the undis- 

 turbed western ends of the red Ordovicic rocks. If the sea encroached 

 here, these later deposits would have a marine aspect, but the fact that 

 fossils are absent in most cases, except for the peculiar Arthrophycus 

 harlani and the "worm" tubes, would indicate that these beds were de- 

 posited above the sea, along river floodplains. Westward, however, the 

 northern series of deposits (the Upper Juniata) were washed into the 

 sea, the shore of which during Medina time did not probably extend much 

 farther east than Rochester. In western Ontario encroachment of the 

 sea began earlier, for here we have the marine Keppel dolomite resting 

 on a surface of Queenston. These dolomites were probably formed while 

 erosion was beginning in the cast and while the early Medina sands were 

 spread by the streams over the old Ordovicic land surface. Then a- the 

 product of this erosion was carried farther westward by repealed rework- 

 ing, it finally entered the sea, which had then advanced farther east. 

 Thus the fossiliferous Medina beds of western New York and the red and 

 green Oabots Head sands which rest on the Keppel dolomite were de- 

 posited. 



As the axes of the anticlines in the east were worn away, the underly- 

 ing Bald Eagle conglomerate was discovered and white quartz sands and 

 pebbles were now furnished to the streams. II should probably he con- 

 sidered that the lilhifieat ion of these bods had not progressed very far. 

 and thai hence the streams did not find it too difficult In obtain the ma- 

 terial. The reworking by streams and winds of these older white quart 

 itea produced the material of the Clinch and Tuscarora. Where streams 

 were active, coarse material was carried along and deposited as quartz 



*■ 11 should be remembered thai under iiiis term 

 >t have been red al the time of the folding. 



