. Geology of the Narragansett basin. Geology. 102 GEOLOGY OF THE NARRAGAlirSETT Fig 3,—Diagram showing misleading synclinal exposures of similar strata. without other means of correlation than these physical criteria, as to which horizon formed the axis of the synclinal structure. Where beds have been stripped off from areas several miles in width, as between the Narragansett and Norfolk County basins, there is difficulty in making- correlations. Owing to denu- dation, the uppermost beds of a formation, as originally deposited, may be entirely lost. Thus there is doubt as to the correl
. Geology of the Narragansett basin. Geology. 102 GEOLOGY OF THE NARRAGAlirSETT Fig 3,—Diagram showing misleading synclinal exposures of similar strata. without other means of correlation than these physical criteria, as to which horizon formed the axis of the synclinal structure. Where beds have been stripped off from areas several miles in width, as between the Narragansett and Norfolk County basins, there is difficulty in making- correlations. Owing to denu- dation, the uppermost beds of a formation, as originally deposited, may be entirely lost. Thus there is doubt as to the correlation of the upper conglomerates near Newport with those in the Taunton syncline. The Newport conglomerates may be in the position of the left-hand syncHne in fig. 3, while those near Taunton correspond to the upper conglomerate in the right-hand synchne. G^LACIATION. The chief difficulty arising from glaciation is the coating of drift which is left upon the rocks of a country. In the Carboniferous field of southern New England the embarrassment from this source is particularly great, for the reason that the area received a thick coating of the deposits of the retreating ice sheet. So effectually are the bed rocks concealed in parts of the Carboniferous basin, that outcrops may not be seen oftener than from 3 to 5 miles in any direction. The tracing of highly inclined strata along their strike can not be safely undertaken in these areas, and the mapping of the formation must be done with reference to the broadest possible gTOups, or perhaps be limited to the indication of the presence of undiscriminated members of a large rock series. The distri- bution of fragments of rock along known lines of glacial carriage is some- times a help in fixing the boundai-ies of the underlying bed rocks.^ In this field the transportation of bowlders was from north to south. Where the rocks trend in bands from east to west^ the line along which each differ- ent kind of rock appears in the drift
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