MEDINA SANDSTONE. 
39 
4. Greenish Grey Argillaceous or Siliceous Sandstone. Grey Band of Eaton. 
Towards the upper part of the Third division, the coloring matter becomes less universally 
diffused, or the deoxidizing process has been more efficient, and spots and lines of grey in¬ 
crease until the greater part becomes of that color. At this stage there is sometimes an 
increase of argillaceous, at others of siliceous matter, and a gradual passage into the upper 
division of the rock. At Lockport, and in some parts of Wayne county, this part of the rock 
is a green marl with spots of bright green shale intermixed. It is generally argillaceous in 
character, though at Lewiston some portions are highly siliceous. The variation from the 
mass below is chiefly in color, and it forms a marked line, contrasting strongly with the dark 
brick-red of the Third division. The intimate connexion of this portion with that below pre¬ 
cludes the idea of considering it a distinct rock, as color is the chief difference ; and this change, 
though often abrupt, is usually gradual. It sometimes contains small black pebbles, which 
appear at first view like organic bodies, but they are never in sufficient proportion to give 
it the appearance of a conglomerate. These may be seen at Medina, and at Lewiston, spa¬ 
ringly scattered through the rock, differing entirely in character from the surrounding mass. 
This division of the rock is very variable in thickness, and in some places scarcely recogniza¬ 
ble. In the eastern part of Wayne county it is about three feet thick, at another locality but a 
few inches ; on the Genesee river it is nearly five feet, at Medina about four feet, at Lockport 
less than two feet, and on the Niagara river it is ten feet thick. 
The intercalation of the grey siliceous mass (No. 2), differing in color and lithological cha¬ 
racters, and the repetition above of precisely the same products as below, reveals a fact of 
great interest, showing that important changes occurred in the condition of the deposits during 
what we regard as a single period. After a long continued deposition of the mud formation 
highly colored by oxide of iron, there was an entire cessation so far as to allow the deposition 
of uncolored or grey and purely quartzose sandstone ; after which, the former red deposit was 
resumed precisely as below. All the circumstances connected with this quartzose deposit 
are interesting, it being the only part of the rock where animal organic remains are found. 
Here we find Lingula, Cytherina and Pleurotomaria in great numbers, besides Bellerophon, 
Cypricardia and Orthoceras in less profusion. The condition of all these fossils, however, 
indicates disturbance in the waters from which the mass was deposited, or rather near the 
close of its deposition. The Lingulae, so far as ascertained, are all of broken or single valves, 
and usually crowded together in great confusion ; the other fossils present the same appearance 
of having been drifted into their present situation. At Medina, these fossils are near the 
upper part of the grey mass, and are not found above; they are here more abundant than in 
any other place, few being seen west of Lockport. The cause of this agglomeration and 
destruction may perhaps be explained by changes which took place in the condition of the 
mass during its deposition, as indicated by appearances near Lockport and elsewhere. These 
conditions seem to have been either the frequent oscillation of the surface; or that the mass 
in which they are imbedded formed at that time a sandy beach, over which the tide sometimes 
