TRANSACTIONS OF SECTION C. 721 



(d) Fine grey clay with quartzite LouKlers about six inches thick. * 



(<') A layer composed of limestone fragments yielding bones of birds, fish, and 



a Jinely jyreserved canine tooth of the brown bear, discovered by Mr. Clarence Fry. 

 (/) A layer of gravel composed of stones foreign to the cave, but occurring in 



the surrounding drift or derived from rock in «Vm within the basin of Allt an 



Uamh. 



5. Interim Be/port of the Oommitlee for Investigating the Structure of a 



Coral Beef. 



TUESDAY, AUGUST % 



The following Papers and Reports were read: — ■ 



1. Landslips in the St. Cassian Strata of S. Tyrol. 

 Bij Miss M. M. Ogilvie. 



This paper deals with the nature of the landslips in the Wengen and Ca.ssian 

 strata, in the neighbourhood of St. flassian in S. Tyrol, and the effect wliich they 

 have pi'oduced in mingling the fossils derived from rocks of different horizons. 



The peculiar liability of these strata to landslips is attributable (1) to their 

 litliological character and stratigraphical relations ; they are soft, easily weathered, 

 earthy tuffs and thin-bedded marls and limestones, while the strata above and 

 below them are composed of much harder rock, dolomitic or volcanic ; (2) to their 

 occurrence at the high altitude of 5,000 to 7,000 feet, and in a region where the 

 ordinary atmospheric agencies may, and often do, indirectly produce most violent 

 effects, due to the sudden swelling of mountain streams and their increased powers 

 of eroding and transporting loose or insecure material. 



If, from any cause whatever, a breach takes origin in a high-lying meadow, 

 either suddenly or gradually, it must inevitably become wider and deeper in the 

 course of years. The essential features in the development of the landslips in 

 Wengen and Cassian strata are admirably illustrated by tlie actual exposures on 

 the Alp of Prelongei above St. Cassian, The turfed ground along the top terrace 

 or ridge is cracked, fissured, and rent into huge irregular ' clods,' which sink in 

 larger or smaller fragments steadily downward and outward ; the streams at the 

 base of this ridge eat backward and undermine fresh portions, at the same time 

 actively carrying oft" the debris and layering it afresh at lower levels. 



The ' Muren,' on the S. side of Prelongei, are great scars, 300 feet high, which 

 were opened up by a series of landslips three centuries ago. As the dip of the 

 beds isto the N.E., these ' Muren' have remained steep, whereas in the case of 

 slips on the N. side, the slipped rock rests as it were on a sliding plane, and must 

 travel slowly downward. The loosened material from each new slip tills up the 

 gap made by the previous slip ; the surface thus becomes raised, and a plane of 

 repose is gradually reached. 



Several highly fossiliferous limestones and marls occur in the Cassian beds ; 

 some in the upper horizons capping the series exposed in the ' Muren ' have yielded 

 most of the fossils gathered over the whole Prelongei and Stuores Alps. For 

 fragments of these fossiliferous beds occur in secondary position in the lower 

 ground where the remains of successive landslips form in some parts an almost 

 continuous mantle over the beds actually in position. 



A lower fossiliferous zone is recognisable at the base of the beds of the ' Muren,' 

 but its precise palteontological value will take some years to determine. To this 

 end the fossils lying loose cannot be used ; only those which luive been so far 

 weathered out in the bedded rock itself can be regarded as secure evidence. This 

 whole series, in which the landslips here and elsewhere have mainly taken place, 

 merit from the fossils contained in them the name of St. Cassian strata, but they 



1802. 3 A 



