LOWER SILURIAN SYSTEM OF EASTERN MONTGOMERY CO. 465 
With the Black river limestone the case is more difficult. In 
truth it is only under favorable circumstances that the Black river 
can be clearly distinguished from the overlying Trenton. In sec- 
tion 46A the Columnaria zone has a thickness of from 7 
to 9 feet and is followed by a conspicuously darker-weathering, 
semi-crystalline limestone with an appreciable stratigraphic break. 
In section 2B the contrast between this zone and the basal member 
of the Trenton substage is even more marked, since in the latter 
section the Trenton is looser grained and weathers darker than in 
the western part of the region. In section 2D there is a decided 
contrast in color between the Columnaria zone and the sub- 
jacent Birdseye, but no stratigraphic break. The two appear to 
constitute one layer, a fact which is also very noticeable at Newport, 
N. Y. in the quarries about two miles north of the village. The 
thickness of the Black river in 2D is apparently only 34 feet, 
and it will be noticed that in this part of the region the massive 
member of the Trenton substage is unusually thick. The lumpy 
structure mentioned by the early New York geologists as a charac- 
ter of the Columnaria horizon at Watertown is its most con- 
stant lithologic character in the present region. The fauna of the 
Black river limestone is of interest. The three fossils Stro- 
Meroceriumiruwscosum, Streptelasma profundium 
and Columnaria alveolata never pass above it. The 
brachiopoda so abundant in the immediately overlying Trenton are 
very poorly represented in the Black river. The most common 
brachiopod of the latter rock, Zygospira recurvirostra, 
is uncommon or lacking in the former. Rafinesquina al- 
ternata may usually be found in small numbers in any exposure 
of Black river well adapted to collection. The obscure bryozoa of 
the genus Stictopora are usually present. Monticuli- 
pora (Prasopora) lycoperdon occurs associated with 
the Columnaria but is invariably the branched form, while in 
the upper member of the Trenton substage where that fossil is 
so abundant it is the hemispheric form that is common. These 
faunal differences between the Trenton and Black river substages 
are constant throughout the region in spite of variations in 
lithologic characters. The affinities of the Black river limestone 
are however with the Trenton limestone and not with the Birdseye. 
