TRANSACTIONS OP THE SECTIONS. 79 



The Belgian formations regarded as Silurian and Cambrian are found in the 

 Ardennes in Brabant, parallel to the Meuse and Sambre, and near Dour in Hainault, 



The Silurian or Cambrian of the Ardennes rests imconformably on the Deyonian, 

 The ill-preserved fossils that have been foimd do not sufficiently determine the a^e, 

 consisting only at present of Dicti/onema and part of a Tiilobite belonging to the 

 genus Paradoxides, which would place it in the Cambrian. The true Belgian 

 Silurians] belong to part of the Rhenan series of Dimiont, in which Silm-ian fossils 

 were found in 1860 by M. Gosselet. 



The Brabant Silurian deposits extend over an area about 70 miles long, the 

 greatest width being 16 miles. That of the Sambre and the Meuse is a strip about 

 40 miles long, and less than two miles wide. 



The Brabant series is divided into four groups, the upper alone of which has 

 yielded fossils, and this alone is represented in the Sambre and Meuse district. The 

 following are the groups in descending order : — 



1. Gembloux series (quartziferous schists). 



2. Oisquezcq series (variegated and graphitic schists). 



3. Tubise series (quartzites). 



4. Blaumont (lower quartzites). 



From the upper series 52 species have been obtained, several of which appear new ; 

 they include Trilobites, Brachiopoda, and Graptolites, characteristic of the upper 

 members of the Lower Silurian, a second stage of M. Barrande, mixed with some 

 Upper Silurian species. 



Synchronism and Foreign Equivalents. — ^With regard to the analogies of the Bel- 

 gian SUurians with those of other countries, the author agrees with M. Barrande 

 that his second stage, represented in the Bohemian district by quartzite, and also 

 represented in almost all Silurian districts, occurs in its ordinary state in Belgium. 

 In England it includes the Llandeilo and overlying Caradoc gioups, and in Ireland 

 the recognized equivalents, while in France, Spain, Portugal, Thuringia, Sweden, 

 Norway, Russia, and North America it is known by vaiious names. It is re- 

 presented in Belgium by the genera Illcenus, Triniicletts, Ampyx, and others. 



Species have also been found referred to Dalmanites, Cheiruriis, Lichas, Caly- 

 tnenes, Acidaspis, Homahnotus, but to groups peculiar to the second stage. The 

 great development of Orthis common in England, Russia, and the United States 

 is also remarkable in Belgium, Cystidea have also been met with. 



On the Formation of Siuallow-Tioles or Pits ivith Vertical Sides in Mountain 

 Limestone*. By L. C. Miall. 



The paper described two kinds of these cavities, one designated " cavities of ero- 

 sion," and the other "cavities of subsidence." A detailed account was given of a 

 singular excavation at the head of Swaledale, typical of the first species. Its pecu- 

 liarities were defined as consisting of vertical, fluted sides, and isolated pillars in 

 the centre of the pits. Falling water, aided by pebbles, was looked upon as the 

 source of excavation, and a thick surface-covering of drift, retentive of moisture, 

 was regarded as an essential feature, the spongy mass discharging the rainfall at 

 certain regular points. Those swallow-holes were next considered whose existence 

 is due to subsidence of an undermined crust ; and many examples were cited and 

 discussed, principally from the moimtain-limestone district of Craven. The eflfects 

 of such subsidences upon superficial deposits (as of glacial drift) were adverted to 

 in conclusion. 



On the Evidences of Recent Changes of Level on tTie Mediterranean Coastf. 

 Bij George Maw, F.G.S., F.L.S., Sfc. 



The author in this paper pointed out, from personal observation, the various evi- 

 dences the Mediterranean coast presents of changes of level, both above and below 

 the existing shore-line, 



* This paper is printed at length in the ' Geological Magazine ' for November 1870. 

 t Printed in cxtenso in the 'Geological Magazine' for December 1870. 



