Yol. 55.] INTO DIABASE AT SOREL POINT (NORTHERN JERSEY). 431 



feature, and one which shows how complete is the penetration 

 effected by the granite. The frequent occurrence of large and 

 small fragments of the basic rock split off and isolated in the 

 granite indicates this even more obviously ; sometimes these are 

 great angular blocks most clearly seen from a distance, at others 

 innumerable small chips, fully appreciated only when close at hand. 



As the state of an igneous rock at the time of its intrusion as 

 well as the circumstances under which this intrusion was carried 

 out are of some interest, one locality, Sorel Point, will be described 

 as throwing some light on these matters. Erom a little distance 

 the rock appears to be an uniform red granite, in which lie a few 

 elongated fragments of the basic rock from about 10 feet long down- 

 ward. A rather closer view, however, shows the acid rock to exist 

 in two forms : the first, a brick-red aplite, smooth on its weathered 

 •surface, fairly coarse, and with conspicuous quartz-grains; the second, 

 less markedly red, and apparently a coarser rock with rather large 

 felspars standing out on its rough weathered surface. The upper 

 part of the section consists of the so-called ' diorite,' and into this 

 the porphyritic granite thrusts wedge-like tongues looking like 

 waves frozen in place. Here and there the more central part of 

 these tongues consists of the red variety, but this is replaced in- 

 definitely by the other. On closer examination the conviction 

 arises that no great distinction as to age can be made between the 

 two varieties of the granite, and it is moreover noticed thut the red 

 variety is either free from, or very occasionally contains, fragments of 

 the basic rock. On the other hand, in the more porphyritic variety, 

 these are constantly to be found: sometimes thickly, sometimes 

 sparsely disseminated, frequently appearing as mere shadowy patches. 

 The composition varies considerably from point to point, in relation 

 with the amount of basic material present. In one case, a softened- 

 looking fragment some 6 inches long lay embedded half in the red, 

 half in the more basic granite, the two passing one into the other. 

 The latter extended round the fragment on the red side as a narrow 

 ^one ; in the same way, when the granite is close to the basic rock, 

 a layer of granite, rich in the dark minerals, is interposed between 

 the two. In one case this measured about 1 inch across, in another 

 3 or 4 inches. The relations of these two varieties of granite to each 

 other are of interest — the more basic or porphyritic forms veins 

 and streaks in the red, the two being closely intermingled, jet 

 Temaining at the same time distinct. At one place this streaking 

 took the form of a V, one limb of which Vi as about 8 feet long by 1 

 broad, the other narrower and less clearly defined. In the centre of 

 the V was the normal or brick-red granite. At the point of meeting of 

 the two limbs the vein thickened out considerably, and here actually 

 enclosed rounded fragments, ±rom 3 inches upward — occasionally 

 lenticular — of the red granite, seemingly unaltered. In these veins 

 or streaks are the usual black patches. 



The occurrence of zones existing between the unaltered red granite 

 and the diabase point to merely local absorption along the line of 

 contact. It is, however, difficult to separate these zones from the 



