KAWA HYBRID ROCK. 137 



This is 2*83 in one case and 2-87 in the other, the mean being 2-85. 

 Now that of the granite (adamellite) is 272 and that of the olivine 

 dolerite or gabbro is 3*00, the mean of which is 2*86, or agreeing 

 with that of the hybrid rock— which is what we should expect. 

 Similar mean values calculated for many of the chief constituents 

 such as the iron (both Fe 2 CX and FeO) magnesia, lime and potash 

 show the same thing and verify the intermediate chemical 

 character of the hybrid rock as compared with that of the 

 granite and dolerite, the exceptions being the alumina and soda. 

 Secondly, the Kawa basic rock in chemical contents agrees better 

 with olivine dolerite, ('aimer (see Hatch : Petrology, p. 221), than 

 with olivine irabbro. The ophitic structure and the nature of the 

 rock as a dyke are also in favour of this. This conclusion then tells 

 against any such supposition as that the Kawa hybrid might be 

 due to ' magmatic segregation." Thirdly, as regards the abundant 

 large plates of bid ite present in the Kawa hybrid, to account for 

 this is essential in any theory of the rock as a hybrid produced 

 by reaction between distinct rocks ; because neither in the coarse 

 normal granite (Idar type) nor in the even, medium-grained dolerite 

 rock of'the invading dyke do there appear any such very large 

 plates of biotite. Apparently d fwpos of such a case as this, Harker 

 (Geology of the Small Isles," Mem., G. S. of Scotland, 1908. p. Ill) 

 savs : " but it can scarcely be doubted that if the granite magma 

 had invaded and incorporated gabbros and diorites as well as 

 eucrites and peridot it es ; biotite would have been a conspicuous 

 product of the reactions." Although our case at Kawa is apparently 

 the opposite of this, inasmuch as it was the olivine dolerite or 

 gabbro that invaded the granite, the nature of the mixture would 

 probably have been the same. 



AHMEDNAGAR (HIMATNAGAR) SANDSTONE SERIES. 



It will readily be seen that the presence of ordinary conglomerate, 



freestone in large quantity and simple shales 



A relatively young j n t ], e composition of this series, together with 



formation. No fossils. ^^ a , m()st un dj st urbcd, horizontal lie, point 



to the series being a relatively young one in the geological history 

 of this part of India. That it also comes very high up among the 

 historical rocks generally, is also to be inferred from several sur- 

 rounding facts that will presently be mentioned. Unfortunately, 

 no determinable fossil remains have been preserved within the 



