PROCEEDINGS 



OF THE 



PHILOSOPHICAL SOCIETY OF GLASGOW. 



MARCH 21, 1860. 



PEOrESSOB Anderson, tlie President, in the Chair. 

 Mr. C. Greville Williams was elected a member of the Society. 



On Tra/p Dykes between Cordon and South End of Whiting Bay, Island 



of Arran. By Mr. James Napier, Chemist. 

 The results of some observations made by Mr. Napier on the trap dykes 

 on the sea-shore between Invercloy and Lamlash Bay were communicated 

 to the Society in 1854. From the composition of these dykes, and their 

 relation to some of the neighbouring trap hiUs, it was inferred that 

 when there are large and sudden upheavals of trap, the rock through 

 which it bursts will have a tendency to crack and fall away from the 

 outburst, and that the fluid trap will flow into the fissures thus produced, 

 and form dykes. Similar observations were made subsequently on the 

 dykes occurring along the shore from Cordon to the south end of 

 Whiting Bay. With the aid of a plan of the locaUty, Mr. Napier 

 described the dykes in detail, and showed that their direction went to 

 confirm the opinion he had formed of their origin.* 



In large beds of trap will be found masses of sandstone so altered 

 by vitrification that it requires a close examination to distinguish it 

 from the trap in which it is imbedded; also curious stratifications 

 of sandstone and trap, as if the sandstone rock had split open hori- 

 zontally in different portions, and the fluid trap had flowed in and 

 forced its way for a long distance, forming complete strata. This 

 circumstance suggests a high state of fluidity in the trap, as it has 

 flowed into some of the finest cracks; and the trap found here would, 

 from its composition, not only fuse easily, but flow easily. There is 

 evidence also in this place in favour of several overflowings, some at 

 very short intervals, as where one layer rests upon another, while 

 others indicate a considerable interval ; not, however, a geological 

 interval, as the whole has probably been eruptions during one period of 

 time. As we proceed from a precipitous overflow resting on sandstone 

 towards Whiting Bay, and down on the level part of the beach, there is 

 a beautiful columnar pavement, where the columns stand on end. The 



• Mr. Napier called particular attention to Kingucross Point, wliere a great many 

 interesting phenomena are seen. 



Vol. IV.— No. 8. 2t 



