Reports and Proceedings — Geological Society of London. 331 



of all proofs of subaerial hydration and the remarkable freshness of 

 the rocks as precluding the possibility of the micropegmatite having 

 been formed by secondary change. The primary origin of the micro- 

 pegmatite he believes to be proved by — (1) the crystal lographic 

 continuity of its felspar with that of the normal plagioclase of the 

 rock ; (2) the mode of occurrence of the micropegmatitej filling in 

 the angles and spaces between the augite and the plagioclase ; and 

 (3) its variation in coarseness of grain agreeing with that of the 

 remaining two constituents of the rock. 



These augite-diorites with micropegmatite are then compared with 

 the granophyric gabbros of Barnavave, Carlingford, described by 

 Professor Sollas, to which the author maintains that his explanation 

 equally applies. He insists that the separation of the acid and 

 basic materials of a magma, which takes place so frequently on 

 a large scale, equally occurs in the midst of a consolidating mass, 

 and combinations such as that described in the paper will be formed. 

 He insists also on the proofs of close genetic relations between the 

 gabbros and " granophyres," and of their practical contemporaneity 

 in the various districts in which these phenomena have been noticed. 



2. " The Laccolites of Cutch and their Relations to the other 

 Igneous Masses of the District." By the Rev. J. F. Blake, M.A., 

 F.G.S. 



The author has observed thirty-two domes of various kinds in 

 Cutch, distributed as follows : (i) those connected with the northern, 

 islands ; (ii) those of Wagir ; and (iii) those along the northern edge 

 of the mainland. They are divisible into four classes : (a) those 

 which are so elongated on the line joining adjacent ones that they 

 seem to be mere modifications of anticlinals, though the supposed 

 anticline is not really continuous; (b) those which lie in a line, but 

 are not elongated in that direction, and often in no other ; (c) those 

 which are related to a fault, which cuts them in half; and {d) those 

 which are not in any particular relation to each other, or to any 

 other stratigraphical feature. 



The domes vary in degree of perfection : some are irregular, 

 while some have the strata running in concentric circles, the outer 

 and newer strata dipping away from the inner and older. In no 

 less than ten of the thirty-two domes igneous bosses are found 

 occupying the centre, and these are distributed amongst all of the 

 above classes. The author gives reasons for maintaining that the 

 domes are the results of intrusion of igneous rocks in the form of 

 laccolites, and are not anticlinal folds which have afterwards been 

 affected by cross-folds. The domes are contrasted with igneous 

 peaks which occur in abundance in a different part of the area, 

 usually at a higher horizon of the strata and at a higher level above 

 sea. These are probably volcanic pipes through which the lava 

 was forced and extruded at the surface. 



The author compares the rocks of the bosses with those of the 

 dykes and flows. Both are principally perfectly fresh dolerites, but 

 the former are distinguished by the presence of intergrowths of 

 micropegmatite as the last stage of consolidation, as in the " Konga 



