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ON THE GEOLOGY OF THE ISLAND OF AQUIDNECK. 753 
the island, where they can be well determined, makes it likely that 
many occur in the region which is so deeply covered with drift 
_ that the observer cannot have a chance of measuring the disturb- 
ances they produce. 
’ _ At-the time when the carboniferous beds of the uppermost part 
_ of this section were formed, the shore at this part of the continent 
= was not far from its present position. The presence of large quan- 
tities of conglomerate with water-worn pebbles in the lower part 
of the same section conclusively proves this point. From the car- 
boniferous sea an arm or bay having a width of from six to ten 
miles extended to the northward, with considerable variation in 
width, as far as Worcester. It is evident that this bay was the es- 
tuary of a considerable river, probably a stream of far greater 
dimensions than,any of those which now empty into Narraganset 
ay. Down this bay there came at successive times large quanti- 
ties of detrital materials which varied much in character during the 
two divisions of the period. During the time of the deposition of 
the conglomerates there was an immense transportation of frag- 
- ments from some points in the interior to this shore region. The 
variety in the chemical and mineralogical constitution of these 
pebbles is, considering the great tendency there is to equalize their 
characters by metamorphism, exceedingly great. Some of the 
materials can be recognized as now in position in the region to the 
northward but by far the larger part are from rocks which do 
hot, so far as known, occur in the neighborhood. The syenite and 
other felspathic rocks of the Bristol Neck sections are found in 
abundance. Other types of syenites also oceur which cannot be 
80 easily referred to any bed rock; some geologists have found 
fragments of Lingule in argillaceous pebbles of this formation. 
ao hese are not known to occur in any rocks to the northward 
_ hearer than the Champlain region; it is more reasonable to be- 
lieve, however, that the source of supply of these fossils has long 
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since been destroyed by erosion, than to suppose that they have 
been transported from so remote a point. It is quite in accord- 
ance with what we know of the erosion of these old rocks to sup- 
pose that great masses of these fossil bearing rocks may have 
been in the immediate neighborhood at the time when these con- 
glomerates were formed and yet these fragments in the newer 
rock remain the only record of their having existed. 
AMER. NATURALIST, VOL. VI. 
