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Meridian Mark


trmcconn
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Before a recent trip to Burlington I scouted out benchmarks in the area for possible recovery and noticed one named "Meridian Mark"  on the UVT campus. It has a pid (PG0858) and shows on the NGS data explorer as a red dot next to a sidewalk crossing one of the many quadrangles, but the data sheet is essentially empty. It only lists a pair of scaled coordinates and no history or recovery reports. I had decided not to bother with it but got desperate after failing to find two "easy" vertical controls mounted in retaining walls that no longer exist. (Something there is that does not love a retaining wall!) So on the way back to my daughter's apartment I diverted down that diagonal sidewalk just in case. There was nothing obvious, but there was a small rectangular patch of concrete flush with the ground next to the sidewalk in exactly the place shown by the red dot on Google Earth. There were no markings of any kind on it, and I decided it was most likely just the remains of an earlier sidewalk or part of the foundation for a vanished lamppost. Still, I wonder... The only thing I could find about Meridian marks is that they are temporary marks used by surveyors for calibration. Anybody have any further information about them?

 

The trip had a happier ending. The next day we decided to do an afternoon hike to the top of "Mt. Philo", an 800 foot drumlin just south of Burlington. It is a nice mellow little hike and the view of Lake Champlain and the high peaks of the Adirondacks from the top is spectacular. I got to thinking "Hmm... Isolated peak in an area with a large amount of historical survey activity. I wonder..." I moseyed up to the exact summit and practically tripped over the monument of triangulation station Philo (PG1937). Sometimes you win a round with the benchmarking gods. (With no cell service I was unable to pull up the data sheet and didn't try to find the reference marks with a random search. But someday, I'll be back!)

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PG0585 is coming back as "Surface Mark Reported Destroyed", and the two entries listed in the datasheet show it's been gone for a while:

 PG0858                          STATION DESCRIPTION
 PG0858
 PG0858'DESCRIBED BY COAST AND GEODETIC SURVEY 1935
 PG0858'IN BURLINGTON.
 PG0858'AT BURLINGTON, CHITTENDEN COUNTY, ON THE UNIVERSITY OF VERMONT CAMPUS,
 PG0858'ABOUT 62 YARDS SOUTHEAST OF THE SOUTHEAST CORNER OF THE FLEMING
 PG0858'MUSEUM, ABOUT 65 FEET NORTH OF THE CENTER LINE OF A CINDER ROAD
 PG0858'LEADING TO THE DORMITORIES, AND 38 FEET SOUTHEAST OF A POLE. A BLOCK
 PG0858'OF GRANITE PROJECTING ABOUT 6 INCHES ABOVE GROUND.
 PG0858
 PG0858                          STATION RECOVERY (1964)
 PG0858
 PG0858'RECOVERY NOTE BY COAST AND GEODETIC SURVEY 1964
 PG0858'SURFACE MARK REPORTED DESTROYED.

 

Interesting statement on the Philo datasheet:

 PG1937'MOUNT PHILO IS A 1-INCH BOLT THAT PROJECTS ABOUT 4 INCHES
 PG1937'AND IS LOCATED DIRECTLY UNDER A SMALL WHITE BUILDING (CARETAKERS
 PG1937'TOOL SHED).

Directly under? Really? :)

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That's weird, because when I download data sheets by PID in DSWorld (PID=PG0858) I only get some boilerplate definitions followed by:

-----------------------------------------------------------------------------
  Pid    Name                           Lat        Lon        Elev      O o Hv
  ------ ----------------------------- ---------- ----------- --------- - - --
 >PG0858 MERIDIAN MARK                 44 28 44. /073 11 50.                XX
 >PG0858 MERIDIAN MARK                 44 28 44. /073 11 50.                NN

 

"Mount Philo" is a different (and older) mark than "Philo". There is no tool shed there now, but I didn't know about Mount Philo when I was there and didn't look for the bolt. Another thing to do on my return visit!

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Both USC&GS and USGS set "Meridian Marks," although only USGS had an actual meridian disk for their work .  Both agencies had robust magnetic observation programs - now largely combined into activities by USGS.  These marks were set to support local land surveyors to be able to determine the magnetic deflection to apply to their compass readings.  Long before we were even a country, the vast majority of property boundaries were determined using a compass.  Even thought the instruments changed in style, the compass was a critical part of surveying until the advent of GPS.  Since any compass reading is highly impacted by local magnetic variations,  USC&GS and USGS engaged in programs to set pairs of stations, typically on the grounds of county courthouses, for which they would determine the magnetic direction and "true" (typically astronomic observation) between the pair.  In many communities it was a requirement for anyone performing boundary surveyors to go to those stations once a year to compare the readings from their instruments to the values published by the government.  This would give them an offset that they could apply to their own measurements to attempt to give the best magnetic direction along any given line they observed.  For a range of reason this effort was abandoned by probably the late 1920s.  These markers are a great example of the nations surveying and mapping history.  A very good example of some restoration efforts was done by the Maryland Society of Surveyors over the pair set at the Fredrick County courthouse https://www.hmdb.org/m.asp?m=89631

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On 8/8/2021 at 7:53 PM, trmcconn said:

That's weird, because when I download data sheets by PID in DSWorld (PID=PG0858) I only get some boilerplate definitions followed by:

 

 

When you have a code that is one of the "Destroyed" codes (X, Y, or Z), you can go here: https://geodesy.noaa.gov/cgi-bin/ds_pid.prl

Put in the PID, and select "Include Destroyed Marks". Then you will get the full datasheet as it was before it was marked destroyed. :)

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In my hometown a stone post was placed in the cemetery, a place without wire fences or water pipes to distort the magnetic field. Later, steel coffins became much more common, so that might not be such a pristine magnetic environment.

True bearings were given to the courthouse peak and a church spire, both of which are now gone so we can't use the bearings.

The stone post is cracked but still there level with the ground as of a couple years ago. I did an OPUS share on it just to perpetuate the history.

https://geodesy.noaa.gov/OPUS/getDatasheet.jsp?PID=BBFS77&style=modern

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The magnetic station in Croydon was set by USC&GS observer W.F. Willis in the fourth quarter of 1901.  See page 125 of the USC&GS Superintendent's Annual Report of 1901

Those are great old stations and I'm glad to see it's well preserved and now part of the National Spatial Reference System.  Regrettably there is no database of these old stations.  Finding data on them can require a certain amount of detective work.

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