Table 2
Roundness #.9 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
.8 |
0.65 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
.7 |
2.29 |
|
1.75 |
|
|
|
3.03 |
6.06 |
|
|
|
|
|
|
|
.6 |
14.54 |
12.5 |
21.05 |
19.05 |
71.43 |
33.33 |
36.36 |
31.43 |
33.33 |
60 |
33.33 |
|
66.67 |
|
|
.5 |
45.26 |
47.22 |
53.51 |
33.33 |
28.57 |
66.66 |
46.97 |
48.51 |
58.33 |
40 |
33.33 |
66.67 |
|
100 |
|
.4 |
21.56 |
23.61 |
21.05 |
38.1 |
|
|
13.64 |
11.43 |
8.33 |
|
33.33 |
33.33 |
33.33 |
|
|
.3 |
8.01 |
9.7 |
2.63 |
9.52 |
|
|
|
|
|
|
|
|
|
|
|
.2 |
4.74 |
4.16 |
|
|
|
|
|
2.86 |
|
|
|
|
|
|
|
.1 |
2.78 |
2.78 |
|
|
|
|
|
|
|
|
|
|
|
|
|
Angular distance miles |
1 mi. |
2 mi. |
2.5 mi. |
3-4 mi. |
4-5 mi. |
5-6 mi. |
7 mi. |
7-8 mi. |
8-9 mi. |
9-11 mi. |
12-13 mi. |
13-14 mi. |
16-17 mi. |
20-21 mi. |
Table 3
|
Group Breakage 3 |
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|
|
|
|
|
|
|
|
|
|
|
|
|
|
2 |
23.84 |
35.44 |
23.84 |
34.13 |
|
|
55.41 |
64.10 |
66.67 |
|
|
35.71 |
|
|
|
1 |
27.84 |
22.78 |
18.58 |
8.69 |
|
|
17.57 |
7.69 |
|
|
|
42.86 |
|
|
|
Distance |
0-1 mi. |
1-2 mi. |
2-3 mi. |
3-4 mi. |
5 mi. |
6 mi. |
7 mi. |
8 mi. |
9 mi. |
10 mi. |
12 mi. |
14 mi. |
16-17 mi. |
21 mi. |
Table 4
|
Round-ness no. |
Granite S |
Gneiss S |
Granite P |
LineatedGranite |
Granite A Gneiss
A |
Pegmatite A |
Pegmatite K |
Quartzite |
Basalt |
|
.8 |
|
2.86 |
|
|
|
2.94 |
2.56 |
7.61 |
|
|
.7 |
1.61 |
5.71 |
|
7.64 |
|
2.99 |
2.56 |
15.38 |
14.29 |
|
.6 |
14.52 |
11.43 |
57.14 |
17.95 |
16.22 |
5.88 |
35.24 |
7.64 |
17.86 |
|
.5 |
12.90 |
5.71 |
28.51 |
35.90 |
37.83 |
23.53 |
23.08 |
23.08 |
42.86 |
|
.4 |
19.95 |
28.57 |
7.14 |
7.64 |
18.92 |
38.24 |
15.38 |
|
21.43 |
|
.3 |
30.65 |
20 |
7.14 |
10.26 |
21.62 |
20.54 |
25.64 |
38.46 |
|
|
.2 |
16.13 |
22.86 |
|
20.51 |
5.40 |
2.94 |
|
7.69 |
3.57 |
|
.1 |
4.84 |
2.86 |
|
|
2.70 |
2.94 |
|
|
|
Table 5
|
Category of
breakage |
Granite S |
Gneiss S |
Granite P |
LineatedGranite |
Granite A Gneiss
A |
Pegmatite A |
Pegmatite K |
Quartzite |
Basalt |
|
3 |
30.65 |
25.71 |
64.29 |
43.54 |
35.14 |
14.71 |
43.54 |
23.08 |
89.28 |
|
2 |
45.16 |
37.14 |
21.43 |
30.77 |
43.24 |
58.82 |
43.59 |
46.15 |
7.14 |
|
1 |
24.19 |
37.14 |
14.28 |
25.64 |
21.62 |
26.47 |
12.82 |
30.77 |
3.57 |
Table 6
|
Shape |
Granite S |
Gneiss S |
Granite P |
LineatedGranite |
Granite A Gneiss
A |
Pegmatite A |
Pegmatite K |
Quartzite |
Basalt |
|
Spheres |
38.71 |
28.57 |
50 |
30.74 |
51.31 |
41.18 |
74.35 |
46.15 |
60.71 |
|
Blades |
11.29 |
8.57 |
|
5.13 |
8.11 |
2.94 |
|
|
|
|
Discs |
37.04 |
57.14 |
27.57 |
35.90 |
32.43 |
17.65 |
20.51 |
30.77 |
25 |
|
Roundness |
12.90 |
5.71 |
21.43 |
28.21 |
8.11 |
38.24 |
5.13 |
23.08 |
14.24 |
Change
of the roundness in the process of transportation
Observation
of boulders indicates that boulders were rounded to a roundness 0.5 or higher
on Krumbein’s scale and then were crushed again. This observation agrees with
Drake’s study of pebbles in which a dynamic equilibrium was observed between
the process of abrasion and crushing. Average pebble was abraded to a roundness
0.5 and then crushed to start the process of rounding over again. For pebble
size particles, the equilibrium around the mean roundness of 0.5 was reached at
a distance of 1mi from the source and then remained through all 21mi of
transportation. In general, the roundness of the pebbles increases with the
distance.The boulders present the analogical characteristic of roundness and
breakage like pebbles. They also develop dynamic equilibrium between breakage
and roundness around mean roundness number of 0.5 but after a longer distance
of transportation respectively to their bigger size. Higher durability of
bigger particles lets them survive through much longer distance than pebbles
can. To reach dynamic equilibrium by boulders between roundness and crashing
around mean distribution of roundness 0.5, the distance of, approximately 15 to
20 miles is needed based on the roundness distribution of granite A (table 4).
The granite A just reached mean roundness of 0.5 because there is still a big
percentage of boulders below the roundness of 0.5. The basalt for example
carried its equilibrium of 0.5 through many miles before it had been deposited
in the Stony Brook area, which is indicated by a big percentage of boulders
with roundness above 0.5 (table 4).
The
breakage of the boulders
The boulders fall into one of three categories of breakage similar to Drake’s (1972) categories for pebbles:
1. Relatively fresh surface breakage, less then or equal to 0.3 on Krumbein’s roundness scales.
2. Worn surface breakage, worn to roundness 0.4 or greater.
3. No indication of breakage.
Boulders from category 3 have covered the longer distance
of transportation because of their rounded shape. Also, because they would
break and would not appear in the category of boulders, due to their smaller
size. Table 5 illustrates that basalt and granite P indicate long distance of
transportation.
Boulder shape was classified according Zingg’s (1935) classification (table 1 and 6). The analyses of distribution of spheres, blades, rods and discs show certain regularities:
1. The rocks, which have covered a higher distance of transportation like basalt, quartzite, granite P and granite A show a higher percentage of spheres.
2. The Blades do not exist in rocks, which came from far distances (table 5 and 6).
3. Discs are more abundant than rods.
These observations agree with Drake’s (1972) study of
pebbles. In Drake’s study, the blades disappear within 9mi from the rock
source, rods and discs extended to 14mi, and spheres persist to 21 mi.
The basalt came from the second most distant source. A large percentage of these rocks have a roundness above 0.5, in general there is no indication of fresh breakage, mostly they are spheres. Blades are not present in the population of these boulders. If the basalt is associated with the Hartford Basin, then there is a possibility that the source for this lithology lies near the shore of Connecticut in the range of 20 to 25 mi
21 % of the studied rocks are represented by granite A, gneiss A and pegmatite A. According to table 4, it looks like these rocks just reach a roundness of 0.5 because a large percentage of these boulders have their roundness below the mean roundness of 0.5. A study of roundness suggests that these rocks covered a distance of 15 to 20 mi. The large percentage of these boulders in our sample population suggests a large source for this lithology. Similar conclusions can be inferred by analyzing the breakage and shape of these boulders (table 5 and 6). Spheres make up about half of the studied population, blades still appear among the samples, and fresh breakage is common.
The closest rocks to the LI shore are granite S and gneiss S. Since, they are 28 % of the studied sample this makes them the most abundant rocks in the boulder population. Their mean roundness number is lower than 0.5 (table 4). They did not yet reach equilibrium between breakage and roundness. Gneiss S has a mean roundness number around 0.4 (table 4) which suggests a slightly longer distance of transportation than granite S with a mean number of roundness of 0.3. According to a seismic reflection map (Lewis and Stone, 1991 fig. 6), the closest possible location of those rocks is situated 6 mi northeast from Stony Brook.
The lineated granite (11% of sample population) has a bimodal population of roundness (table 5). This may be an indication of a double source of these rocks. One source should be located close to the Connecticut shore as indicated by a mean roundness of 0.5 with higher numbers of 0.6 to 0.7. The second source is close to the LI shore as indicated by a roundness of 0.2 and the existence of blades.
Bimodal populations are also observed in quartzite and pegmatite K. This situation may be possible because pegmatites may be associated with any rock described above with an exception of basalt. Pegmatite K has all the characteristics of pegmatite A except that it lacks garnet. On the other hand, in boulders this pegmatite shows contact with pegmatite S. This observation suggests that part of the population of pegmatite K is actual pegmatite A without the garnet. This explanation agrees with the bimodal distribution of roundness for this lithology (table 4).
The
other types of boulders found on the Stony Brook campus are not discussed
because there were not enough samples found of these rocks.