492 Mtt. H. W. MONCKTON ON THE STIRLING DOLERITE. [Aug. 1 895, 



same. It was interesting to learn that the Stirling dolerite was not 

 a single mass, but a group of sills ; and he thought that the careful 

 study of these intrusive basic rocks was likely to be valuable. 



Mr. Httdleston said that, thanks to the hospitality of Sir James 

 Maitland, he had seen a portion of the district described by the 

 Author, and was glad to confirm, so far as his knowledge extended, 

 the relations of the dolerite to the adjacent strata. He did not 

 quite gather how far the rock was to be regarded as intrusive, or, if 

 intrusive, at what period. 



Sir James Maitland said that he knew the district, and thought 

 that the paper would throw light on the conditions under which 

 basalt cooled. In Milnholm Quarry the basalt showed a fine- 

 grained structure at the upper and lower edges, while as the 

 position retreated from one or other the size of the grain increased. 

 The general dip of the basalt is 1 in 10, while that of the strata is 

 1 in 11 ; thus the basalt cuts very slowly through the stratified 

 rocks and is clearly intrusive in the Coal Measures, for the same 

 bed can be traced and junction-sections obtained with the upper 

 and lower surfaces of the sheet. 



Mr. Rijtley asked the Author for further information concerning 

 the occurrence of the tachylyte. Skeleton-crystals of magnetite, 

 such as the Author described, were not uncommon at or near the 

 margins of intrusive rocks, but in some cases, where the vitreous 

 selvage was poorly developed, spherulitic structure sometimes 

 occurred unaccompanied by skeleton-crystals of magnetite. 



The Author, in reply, thanked those present for the kind way in 

 which they had received the paper. He had no doubt that the 

 Stirling dolerite was an intrusive rock, but all one could say as to 

 its age was that it was newer than the Carboniferous Limestone 

 Series, and older than the long faults and dykes which cut it. 



