288 C. SCHUCHERT MEDINA AND CATARACT FORMATIONS 



The Medina formation as here restricted may be described as follows ; 



Thorold memher or gray band. 2 to 8 feet thick. This is nearly always 

 a white, cleanly washed, more or less resistant, thick-bedded sandstone. 

 Xo fossils are known from it other than the sand fillings in sun-cracks, 

 which are more or less water-rilled, such as are seen at Medina and were 

 described by Conrad in 1838 as Dictuolites hecl'ii. 



The Upper Medina is composed of red, cross-bedded sandstone, more 

 or less impure intraformational shale pebble conglomerates, and some red 

 shales, with a thickness of from 8 to 15 feet. These beds are marked by 

 the burrows Dcvdalu^s archimedes and Arthrophycus alleghaniense. 



The Middle Medina consists of thin-bedded sandstones and shales, 

 more or less red in color, with some white sandstones. The amount of 

 coarse sand is variable in the sections, most abundant east of Lockport, 

 and with more shale at this place and at Niagara. The thickness in east- 

 em sections is about 20 to 25 feet and about 10 feet at Xiagara, where 

 there is, however, no ba^al sandstone. The Medina brachiopod and mol- 

 luscan fauna listed elsewhere is from this zone, and especially from 

 Medina. A. alleghaniense may occur in the upper half of this zone. 



The Loicer Medina is made up of basal, thick-bedded, coarse, cross- 

 bedded, more or less red and dirty sandstones, though in places white and 

 fairly clean. Thickness, about 20 feet. This rests with a very even base 

 on the Queenston. Fossils are very scarce and of no significance. 



THE MEDIXA FAry.i 



Because of the sandy, shifting nature of the Medina formation the 

 fauna, of a very shallow sea, is not a large one. Lingula- cuneata is often 

 found in pure white sandstones and always a.< single valves washed about 

 by the waves. Very little else is found associated in such de|X)sits, though 

 a bivalve may also be present and as well Iwchilinu cyUndrica. In less 

 clean sands the vertical spiral or lamellar burrows of Da'dalu.'i arcliiwedes 

 occur in great quantity; but as a rule this form and Arthrophycus alle- 

 ghaniense prefer dirty sands, while the latter and the so-called fucoids 

 are mest often seen in the dirtiest of sandy beds in thin shale partings. 

 The bivalves and ostracods also preferred the dirty* sands, but all have 

 been washed about by the waves, while the calcareous shelled brachio- 

 pods. ga.'itropods. and cephalopods occur in very thin zones that are more 

 or less limy, though dirty and sometimes even decidedly ferruginous. 



The fauna was originally described by Conrad^^ and by Hall,^^ and is, 

 with subsequent additions, listed below. Some of the species listed by 



1* Second and Third Rept?.. N. T. State Geo!.. 1838 and 1839. 

 i» Geol. N. Y.. Fourth Dist.. 1843. pp. 36-57. 

 Pal. N. T., vol. II. 1852. pp. 4-14. 



