MICHIGAN ACADEMY OP SCIENCE. 
91 
THE BASIN OF ANDERDON LIMESTONE, 
of which the Amherstburg quarry property forms the central area. 
Thus far — except in viewing the entire distance of the Transitional — • 
only the Malden Valley of Anderdon beds has been considered, by 
way of which the supply of this limestone seems to have come in from 
the south’ard. 
The Amherstburg Quarry basin of Anderdon limestone is an expan- 
sion of the Malden Valley, circular in form, with a bulging western 
side. It seems to have had no other communication with the outer sea, 
in Anderdon time, than this valley. Cross sections will show the man- 
ner of deposit to best advantage. Two will suffice, one from east to 
west, and one from UST. x NW. to S. x SE. Test* holes 26, “3,” “8, v 
and 21 are from east to Avest in order. No. “8” is as nearly as may be 
the center of the basin. No. 26 marks the eastern limit of the deposit, 
No. 21 is 1,500 feet Avest of this center and No. “3” is 1,350 feet east 
of center. Were there one more test made as far Avest of center as 
No. 26 is east of it, at the rate at Avhich the depth lessens westward 
there would probably be about the same depth of Anderdon beds in 
that as there is in No. 26. 
No. 20 test was the most Avesterlv put down and though somewhat 
out of line for this cross section is yet available for comparison. (It 
is also interesting as establishing a bulging Avest side.) 
Anderdon at 26, 1' 3", 
Anderdon at “3,” 16' 7", 
Anderdon at “8,” 28' 0", 
Anderdon at 21, 15' 9", 
Anderdon at 20, 6' 2". 
This section shows an east and west shoreing up of Anderdon high 
grade limestone. 
A MODIFIED ANDERDON. 
During Anderdon time, and while these beds were being deposited, 
extraneous influences Avere exerted upon the Anderdon material about 
the outer edges of the basin, sometimes reaching across its full Avidth — 
or rather would I say, meeting in the centre. Just Avhat these influences 
were is not so easy to say. The effect exerted is very palpable. In 
some cases several feet in depth of the Anderdon beds are reduced to 
the quality of an ordinary good limestone; in other cases a silicated 
limestone Avas produced; in still other cases the sIoav depositing lime- 
stone has been swamped with magnesia and silica until a dolomite 
resulted. Whether the magnesia and silica Avere due to an inwash 
from a Silurian sea to the west, north, northeast and east, facilitated 
by a lowering of the confining Silurian anticlinal dam by earth move- 
ments from time to time, alternating with unlift; or Avhether the source 
of the extraneous matter was a Silurian land area, may be open to 
question. Very considerable depths of unmodified pure Anderdon lime- 
stone alternate with deteriorated parts. Especially is this true toward 
* Plain figures indicate tests of the survey of Sept, to Dec., 1910; figures in quotation indicate tests 
of 1909 survey. 
