NIAGARA FALLS AND VICINITY 93 



monioiis with the preceding ones, were laid down on the eroded 

 surface. This was repeated a number of times, as is shown by the 

 succession of changes in the sandstone layers.^ This structure is 

 sometimes shown on a large scale, as in the case of a bed shown 

 about 200 feet north of " Milk cave ravine ", the second of the small 

 ravines met with in coming from the north. Here some of the lay- 

 ers are very gently inclined, and may be traced for some distance. 

 They are obliquely truncated, other horizontal beds resting on the 

 truncated edges (fig. 20b). (Sec also plate 14) 



Fig. 20 b Contemporaneous erosion and deposition in Medina sandstone, Niagara gorge. 



The Medina Lingula (L. c u n e a t a) is found in these sand- 

 stones as in the lower ones, but other fossils are rare. Occasionally 

 on the sections the hollows left by the removal of the shells may be 

 seen^ while similar cavities, caused by the removal of small black peb- 

 bles like those found in the lower layers, also occur. In the upper 

 portions of this mass, on the under side of some thin sandstone lenses 

 resting on and separated by shaly partings, occurs the so-called 

 " jointed seaweed " of the Medina formation, known as A r t h r o - 

 p h y c u s h a r 1 a n i, and illustrated on plate 16. This is a char- 

 acteristic Medina sandstone fossil, but in this region it has not been 

 found in any of the other sandstone strata. Specimens of this fossil 

 were obtained in digging the great power tunnel at Niagara, but 

 only from the sandstone layers near the bottom of the tunnel, which 

 is about the horizon in which they are found in the gorge section.^ 



6 The highest member of the Medina in this region is a hard, 

 massive bedded and compact quartzose sandstone similar to the 



^Compare with this the cross-bedding structure shown in the uncon- 

 solidated sands and gravels in the Goat island gravel pit, and in the section 

 of the old Iroquois beach at Lewiston. 



'The restriction of this characteristic Medina fossil to these upper layers 

 of sandstone at Niagara was pointed out to me by John MacCormick, the 

 watchman of this part of the road, who collects these specimens and keeps 

 them for sale. As he is continually handling these rocks and has handled 

 them for years, he has become famihar with their characters, and is there- 

 fore in a position to obtain knowledge of such facts. 



