Vol. 55.] INTO DIABASE AT SOREL POINT (nOETHERN JEESEY). 439 



ments de feldspaths et de quartz vermicule.' ^ In the slides this is 

 perhaps best seen in the secondary grains into which the felspar is 

 resolved, but it often occurs as a border to part of a felspar which 

 has not been thus altered. 



The fragments included in this intermediate rock sometimes consist, 

 as before mentioned (p, 435), o£ perfectly recognizable diabase, and 

 a thin section of such an one shows that no change has taken 

 place which can be ascribed definitely to the action of the acid 

 magma. Traces of augite are not common in the slide, but are 

 found here and there embedded in the brown hornblende which 

 has for the most part replaced them. Like in some other sections, 

 this is arranged subophitically as regards the plagioclase. The 

 latter is for the most part fairly fresh, and is present in the nsual 

 long, lath-shaped, interlocking forms. The hornblende exhibits 

 locally a rather granular habit, and has occasionally given rise to 

 chlorite. A little apatite and magnetite complete the section. 



(b) Diabase with Material derived from the Granite. 



Passing from the rocks where the acid element is the more 

 conspicuous to those in which it is less so, there will be noticed 

 first, a dark, rather mottled rock which on a casual glance might be 

 mistaken for a normal diorite or diabase of a rather fine texture. 

 It is found in some quantity near the mass of intrusive granite 

 described on p. 432 from La Houle. A closer inspection shows that 

 a considerable quantity of a brown-red felspar is present with 

 some quartz, the latter mineral sometimes occurring in large rounded 

 grains surrounded by narrow rings of small hornblende-crystals. 

 This is far from uncommon. Although the proportion of the two 

 elements is constant throughout the whole specimen, yet they can 

 be seen to be very intimately interstreaked or interveined one 

 with the other ns though not quite perfectly mixed. In a thin 

 section the same arrangement of the constituents is apparent 

 with a little care, even if not at the first glance. Patches here and 

 there are very rich in orthoclase and quartz, both exhibiting the 

 characteristics which have been mentioned before. The former 

 appears late in consolidation, encloses crystals of hornblende and 

 mica, and may be seen to form a kind of matrix for the other 

 minerals. These, if felspar, are often corroded, a point not without 

 importance. The quartz bears the same relation to its surroundings 

 as does the orthoclase. In those parts where the ferromagnesian 

 constituents are conspicuous, orthoclase is absent, quartz very rare. 

 No trace of augite remains in this section, though an irregularity 

 of colour occasionally seen in the larger plates of hornblende may 

 be perhaps regarded as a trace of its former existence ; frequently 

 the hornblende is found in granular aggregates associated inti- 

 mately with flakes of a bleached and rather fibrous brown mica. 

 The felspar, crowded with alteration-products, typically with a 



^ • Mineralogie de la France & de ses Colonies,' vol. ii (1897) p. 36 & fig. 26. 



