There seem's to be more of these being found!!
If this has been posted befoe"I am sorry Mod's" I looked and couldn't find anything on it in the archives.

June 28, 2006 — A group of granite blocks along a grassy Amazon hilltop may be the vestiges of a centuries-old astronomical observatory — a
find archaeologists say shows early rainforest inhabitants were more sophisticated than previously believed.
The 127 blocks, some as high as 9 feet tall, are spaced at regular intervals around the hill, like a crown 100 feet in diameter.
On the shortest day of the year — Dec. 21 — the shadow of one of the blocks, which is set at an angle, disappears.
source:
dsc.discovery.com...