The Silverdale Boulders (Silverdale, Auckland) EarthCache
The Silverdale Boulders (Silverdale, Auckland)
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For almost forty years commuters driving between Orewa, and Silverdale have been intrigued by a set of huge spherical boulders at the side of the intersection leading to the Whangaparoa Peninsula.
The boulders, ranging from about 10-feet in girth diameter down to about 3 feet, were the subject of considerable controversy and discussion when they were first discovered in 1971. At that time, a new motorway was being constructed between Silverdale township and Orewa and the main obstacle in the way was the Silverdale Hill. As the bulldozer and big Euclid front end loader made their first cut into the crown of the hill they encountered a clustered set of about a dozen large concretion boulders. Thereafter, the bulldozer and digger drivers had to cut away the soil surrounding the stones in order to expose them. Later the boulders were shunted down to the western side of the hill where they were placed clear of the work area.
But there was a lingering and exasperating problem that needed to be resolved. The huge spherical boulders were "concretions", which can only "grow" in a sea sedimentary environment over millions of years. In some respects they grow like a pearl will grow in an oyster. A small stone or shell lying in the sea mud becomes coated with a thin layer of lime and sand, which then hardens over time. A second layer coats over the first and so-on until the original object potentially sits at the centre of many hundreds of coated layers.
As so often happens over millions of years, the sea floor can then be pushed upwards and become a part of dry land. However, the boulders will still be found sitting within the same lime and sand rich material from which they were formed. If they're found to be sitting amidst clay or other foreign material not conducive to their formation and growth, then chances are are they've been moved, by some means, to that new location.
This was one of the controversies that raged for a few days in the media in 1971. The visual evidence suggested that it was by ancient human intervention that the boulders had found their way from a suitable incubation environment within sea sediments to the top of this high, inland, yellow-clay hill. Workman were mystified about the out-of-place presence of the boulders and asked the Ministry of Works overseer, Clarry Neville how the stones got there? Mister Neville had no answers and simply replied, 'Your guess is as good as mine'.
Another factor noted by individuals inspecting the boulders, then and since, was that some were heavily incised with geometric patterns. It was quite obvious that humans had, at some remote era, cut designs into the surfaces of a number of the stones. It was equally evident that this concretion arrangement had been long abandoned, as so much soil had built up around them that they were fully buried when the Ministry of Works happened upon them in 1971.
Clarry Neville, was interviewed by newspaper reporters and asked about the anomalous boulder find. Mr. Neville stated that he was mystified as to how they got to the top of the hill. He stated that geologists, were going to investigate the matter and write up a detailed report, but the idea died a natural death and no satisfactory explanation was ever forthcoming from our experts.
To log this EarthCache, you must do the following and email us the results. You can go ahead and log your find, (ie. you don't need to wait for permission) but if we don’t think you have honestly completed the required tasks we will delete your log (after emailing you first of course):
1) Measure the height, width, depth and circumference of the two boulders. Email me the answers.
2) Descibe to me the texture of the surface of the boulders, do you see any patterns? If So, tell me. Email me the answers.
3) Take a photo of yourself, and GPS with the boulders in the background. Please post the photo with your online log..
Please email me this info, please DO NOT post it with your log. Just post your photo.
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