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 tlie eastei'n 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 imtil 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 chnrac- 

 teristics of extrusive sheets, while the western trap range as consistently 



