山竉

山窿係自然形成、喺山裏面嘅中空部份，係一啲嘅好大竉，通常大到可以畀人或者動物入去。好耐以前，原始人會喺度住。書面亦叫穴。

形成 
山竉形成方式可能係水嘅侵蝕作用，又或者係風同微生物等其他外力嘅風化作用。好多自然形成嘅山竉係喺石灰岩地帶，稱之為溶洞。

分佈 
幾乎全世界都可以搵到山竉。

拎 
 Australian Speleological Federation (ASF), AU
 British Caving Association (BCA), UK
 Classification of Caves A list of cave types with links to further information
 Journal of Cave and Karst Studies
 National Speleological Society (NSS), US
 International Union of Speleology (UIS).
 Speleological Abstract (SA/BBS) An annual review of the world's speleological literature.
 The Virtual Cave Photographs of many types of caves.