204 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



the limestone rocks of that locality, which he attributes to the 

 chemical effects of rain-water acting upon the surface. 



These Carniola cavities must not be confused with the 

 "dolinas" or "swallow-holes," which are of common occur- 

 rence in many limestone areas. The latter are explained as 

 insinkings of the surface which have taken place after the sub- 

 jacent mass of limestone has been undermined by subterranean 

 caverns. Recent geological writings have shown that dolinas 

 pre-eminently occur along natural joints and fault-planes, into 

 which surface-water readily passes. 



While dolinas, Carniola cavities, and " Karrenfelder" are 

 forms of erosion limited to limestone mountains or table-lands 

 whose rock is firm and compact, the so-called geological 

 " organs " or earth-pipes (sand-pipes, sink-holes) occur chiefly 

 in plains whose rock-material consists of soft, fissured lime- 

 stone, calcareous conglomerate or gypsum. They are cylin- 

 drical or funnel-shaped cavities, generally upright in position, 

 and filled partially or wholly by loam, mud, or sand. 



Sand-pipes were first described by Brongniart and Cuvier 

 (1811) from the neighbourhood of Paris, and were called 

 "Puits Naturels." In 1813, Mathieu described similar pipes, 

 narrowing towards the base, at Petersberg, near Maestricht, 

 and he called them " Orgues geologiques," the name which 

 is still commonly used. Other writers of that time, Gillet- 

 Laumont and Bory, explained them as due to the solvent and 

 mechanical action of water, infiltrating from the surface, but 

 this idea was contested by later writers, and various erroneous 

 explanations were offered. Lyell and Prestwich examined the 

 earth-pipes and sack-shaped depressions in the chalk of the 

 south of England; and they proved beyond doubt that these 

 hollows had been eroded by the chemical action of surface 

 water rich in carbonic acid, which had primarily found its 

 way along any surface crack, or the fine tubular perforations 

 formed by the root-growths of the surface vegetation. The 

 infilling of sand and clay was derived from the surface layers 

 and soil. 



In the Bavarian plain, Penck's recent researches on the 

 glacial and interglacial deposits have brought to light many 

 fine examples of sand-pipes occurring in the nagelflue or 

 rough limestone conglomerate deposits laid down by glacial 

 floods. Penck thought the sand-pipes had been hollowed out 

 during the period when the nagelflue presented a surface 



