Vol. 5 4. J KEV. J. F. BLAKE ON THE LACCOLITES OF CUTCH. 1& 



* stratified traps/ There were also areas here, especially to the 

 south, where escape was impossible and domes were formed. 



The Author observes that his conclusions, if correct, may be 

 applied to explain the source of the Deccan trap without eruptive 

 centres. It may have been forced out from innumerable orifices as 

 from a sieve, none of these being so much larger than others as ta 

 make a definite centre. 



Discussion. 



Mr. "W. W. Watts congratulated the Author on abolishing the 

 mushroom-stalk-like dyke which disfigured most diagrams of lacco- 

 lites, but failed to understand that the diagrams exhibited by 

 Prof. Blake showed the typical structure of these igneous masses. 

 Indeed, the whole of the sedimentary rocks of this region were 

 represented as floating on a mass of igneous rock. He pointed out 

 that in the Shelve and Corndon area the igneous rock occupied 

 several positions — anticlinal spaces, arch-limb spaces, fault-planes, 

 and twist-lines. The physical structure of the region, however, was 

 just like that of areas from which igneous rocks were absent, making 

 it clear that the structure was the result of lateral pressure, but 

 that an igneous magma was at hand which welled up into all th& 

 regions of lower pressure. It was interesting to note that the rock- 

 types of the laccolites described by the Author corresponded with 

 those described in British masses, and not with those whose petro- 

 graphy had been the subject of the recent memoir by Whitman 

 Cross, published in the 14th Annual Eeport of the United States 

 Geological Survey. 



Mr. Etjtlet said that he felt the limited time allotted to the 

 reading of the paper had prevented the Author from doing justice 

 to his work. After emphasizing the relation of the terms ' peg- 

 matitic ' and ' micropegmatitic,' he suggested that it would be well 

 to supplant the latter by ' micrographic,' as employed by Harker, 

 restricting the term ' graphic structure ' to the well-known coarse 

 intergrowths of quartz and felspar which are at times associated 

 with pegmatite proper or ' Hiesengranit.' 



The President and Gen. McMahon also spoke. 



The Afthoe replied that the points raised by those who had 

 discussed his brief resume would all be found dealt with in the 

 paper itself. 



