Geohjfy wtd Geography. 423 



Section C. — Geology and Gkogkaphy. 



Professor Jameson in the Chair. 



Mr Dunn exhibited and described his new clinometer. 



Mr James Bryce read a notice of some caverns containing bones 

 near the Giants' Causeway. 



Mr Horner, in reference to the same subject, read a communica- 

 tion from Mr Thomas Andrews, of Trinity College, Dublin, who 

 had recently discovered some extensive caves in the Island of Rath- 

 lin, situated four miles from the Antrim coast, with a sea of thirty 

 fathoms between. From the situation of the caves in Rathlin, it is 

 evident that the sea must have once entered them at a much higher 

 elevation than its present level. 



Professor Phillips, in reply to a recommendation of the meeting 

 at Cambridge, gave a general statement of his views of the relation 

 of joints and veins. Rocks are too commonly considered merely as 

 stratified or unstratified, though certain remarkable parallelisms in 

 slate rocks, and the pillar form of divisions of trap-rocks, are too 

 obvious to be left unnoticed by those who attend to the structure 

 of rocks. Professor Phillips states it as a general law, that besides 

 the planes of stratification, there is in stratified rocks another struc- 

 ture — a series of divisions more or less regular, often called joints. 

 These are of various kinds. 



1. Cracks \diich do not go through a whole bed of stone. Some 

 of these called by the workmen dry cracks, have their surfaces of- 

 ten marked by dendritic appearances, occasioned by infiltrated ox- 

 ide of iron, manganese, and other substances. Generally the sides 

 of a crack are in apposition, but sometimes separate. 



They are sometimes empty, sometimes filled with carbonate of 

 lime, or other substances. That they have been produced since the 

 bed was deposited, is easily proved ; for the cracks sometimes di- 

 vide shells, that must have been included in the limestone rock be- 

 fore the crack was produced. In the Rigi also, on examining 

 the conglomerate, we find pebbles of various kinds, which are cross- 

 ed by fissures or cracks, splitting them through and through. The 

 stony matter interposed must be of later origin than the formation 

 of the crack, and still more subsequent to the deposition of the rock. 

 Metallic substances of the same kinds as those which occur in mi- 

 neral veins, are often found in these cracks. 



2. Joints which go through a whole bed, or through several beds, 

 and even through the whole of the conformable beds. Where a 



