Pa 
MUSEUM OF COMPARATIVE ZOOLOGY. 135 
the accordance of the bands in the various amygdules with the bed- 
ding of the adjacent sedimentary layers demonstrates the eruption of 
the igneous sheet before the deformation of the whole mass; but 
manifestly it does not bear on the manner of its eruption. 
The microscope reveals a marked decrease in the coarseness of the 
texture of the trap upwards as the overlying sandstone layer is ap- 
proached at the eastern end of the railroad cut, and a corresponding de- 
crease in the freshness of the rock ; but the texture nowhere becomes so 
fine as that on the back of Gaylord’s Mountain. The intermediate 
sandstone at the south end of the cut contains fragments of amygdaloi- 
‘dal trap in abundance, often water-worn ; but a little distance to one 
side, this mixture is replaced by a strongly marked tufa bed in the same 
horizon, resembling in color and appearance the lapilli from the ash and 
bomb deposit in the Lamentation anterior, locality 8; under the micro- 
scope it shows decomposed fragments of glassy trap in a cement of 
calcite and chlorite with occasional fragmental grains of quartz and 
muscovite. 
The upper trap sheet does not present significant features in the 
railroad cut, but descending to the river and crossing by the road bridge, 
where its upper surface is apparently found, several exposures occur a 
little way up stream, in which there is the usual mixture of trap frag- 
ments with the sands of the sandstone that overlies the sheet. This is 
| thought to be the upper surface of the upper anterior sheet, because no 
other trap outcrop is to be seen until the base of the heavy main sheet 
is reached. 
The breccia in the middle of the cut resembles the breccias of the 
Meriden quarry, but is much narrower, being only four to six inches 
wide. It is a fissure in the trap, on which some slight faulting has 
taken place, as is shown by slickensides ; it is filled with a mixture of 
sand and angular trap fragments, and was undoubtedly formed posterior 
to the production of the trap. 
5.— Conclusions. 
It is difficult for those who have become convinced of the correctness 
of a certain conclusion to state in an impartial manner the evidence on 
which the conclusion rests. We shall therefore not attempt to review 
all the evidence presented above, but will briefly call attention to the 
uniform association in the eastern trap ranges of the numerous charac- 
teristics of extrusive sheets, while the western trap range as consistently 
