Try kettle stones - two words. There's a great write-up on the site for Kettle Stones Provincial Park in Manitoba, Canada. Explains in detail and with illustrations how they were formed and more information about them.
gov.mb.ca/conservation/parks/popular_parks/popular_parks/kettle_stones/info.html
"Kettle Stones"
"The kettle stones' long development spans millions of years. Scientists believe that the stones formed in three stages beginning in the Cretaceous Period, between 70 - 135 million years ago. The first stage took place near the shore of a shallow sea that covered the area during the late Cretaceous Period. Sand from rivers and shoreline erosion, and other marine sediments, were deposited in horizontal layers on the seabed which through time became a stratum (layer) of sandstone."
(Figure 1.1). "Known as the Swan River Formation (SRF), this stratum is 100 m (metres) thick in places."
Figure 1
Figure 1.1: "70-135 million years ago: Swan River Formation (SRF) sand and clay deposited in a shallow sea."
Figure 2
Figure 1.2: "1-70 million years ago: Sandstone concretions formed by chemical precipitation of calcium carbonate."
Figure 3
Figure 1.3: "8,500 years ago: Sandstone concretions emerge from surrounding Swan River Formation (SRF) by Lake Agassiz wave action and Lake Agassiz sand (LAS) was deposited."
Figure 4
Figure 1.4: "Present surface: Following the drainage of Lake Agassiz the land surface emerged and was colonized by vegetation."
Figure 1: "Formation and emergence of the kettle stones, based on concepts suggested by Gaywood Matile, Manitoba Geological Survey."
"During the second stage, regional uplift raised the stratum above the level of the sea. At this time, percolating groundwater cemented loose bits of sand and sediment together to form concretions (Figure 1.2). Sand was cemented around a nucleus or centre-an unknown base, possibly a fossil. The "glue" or adhesive was a lime solution, derived from the calcium carbonate of sea animal skeletons. In this process called chemical precipitation, the concretions maintained the layered appearance found in the original stratum."
"In the third and final stage-about 8,500 years ago-glacial ice of the last Ice Age had retreated into northern Manitoba. Lake Agassiz modified the land to look much like it does today. During the final drainage of Lake Agassiz, beaches, offshore bars and spits formed where the kettle stones were held in the soft sandstone. Waves crashed against the sandstone shore and eroded the loose material around them (Figure 1.3). The harder concretions or kettle stones were left behind with Lake Agassiz sand (LAS). Being firm and round, the stones weren't noticeably altered by the waves. Since then, wind, rain, heat and cold have weathered those that are above ground level. Some appear to be partly above the ground surface and an unknown number of others may be still completely buried (Figure 1.4). The remaining original sandstone stratum is about 10 m below the present sandy surface and extends through all of southwestern Manitoba."
"Wave erosion by Lake Agassiz has left a unique landscape, with the kettle stones propped up like sentinels overlooking the Manitoba Lowlands to the east. While the origin of the name kettles is unknown, it is generally believed that they are so named because they resemble household kettles or kettle drums."
You'll have to visit the site to see the photos and diagrams and further info.
