On Genesis of the Granite Pits on Top of the Dayangshan Mountain of Jinyun County, Zhejiang Province
浙江缙云县大洋山石鼓尖花岗岩坑穴成因

On top of the Shigujian Peak(1477 m asl) of the Dayangshan Mountain in Jinyun County,Zhejiang Province,large amounts of granite pits with diameters ranging from several dozens of centimeters to one meter,and depth from 10 cm to 45 cm are found on the rock surface.These pits mainly appear on the NE and SE sides,and their discharge outlets are in the same direction.The identification results through micropolariscope and X-ray fluroscence spectrometer reveals that the bedrock of pits is from middle to fine-grained moyite being apt to be weathered and mudified.In Dayangshan region the annual mean temperature is 9.2 oC and the annual precipitation at over 1700 mm.On the one hand,there always experiences a period of periglaciation with temperature oscilating near 0 oC for 4 months from December to next March as a consequence,the freezing-thawing cycles may be remarkable to disintegrate the bedrock.On the other hand,the windward slope of Shigujian Peak meets typhoon of over force 10 on the Beaufort Scale in summer,therefore,the blowing makes suspending sands or pebbles grind in swirling form.Based on field investigation and periglaciological geomorphogy,the pits on top of the Shigujian Peak is attributed to frost weathering of periglaciation.Meanwhile,storm and strong wind accelerate the process.Observation shows that both the actions are still undergoing and variant directions of wind aree the main cause for making different shapes of the pits.Because the top of the Shigujian is 1500 m lower than the present snow line,some scholars consider that "glacial pothole" formed in the Quaternary is untenable,even though in the Quaternary Glacial Maximum.