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SOME NORTH-OF-ENGLAND DYKES. 247 
Prats XIII. 
Fig. 1. Tynemouth dyke. WNicols crossed: x20. A portion of one of the 
granular aggregates of anorthite is represented in the bottom right- 
hand portion. It is partially zoned with felspar, having different 
optical properties; but this zone is not continued between two con- 
tiguous grains of anorthite. Two amygdaloids occur in the top left- 
hand portion of the figure. The outer zone of the larger amygdaloid 
is formed of quartz. The ground-mass is composed of long lath- 
shaped felspars, bright-coloured augite grains, and dark interstitial 
matter, which is nearly opaque in this section, even when viewed with 
ordinary light. The figure illustrates the typical structure of the 
Tynemouth and related dykes, 
Fig. 2. High-Green dyke, High Green: x30. Ordinary light felspar, augite, 
and ilmenite. Structure that of a typical diabase. Brown tint of 
the augite somewhat exaggerated. 
Discussion. 
The Presipent remarked upon the exhaustive treatment of his 
subject by the Author. 
Mr. Torey pointed out that very little had been done by previous 
authors in describing these dykes. He said that in the Acklington 
dykes chloropheite had been detected for the first time in England. 
Some of the dykes are probably of Miocene age, while of others 
the age is doubtful. The question of the absorption of the aqueous 
rocks by igneous rocks, especially basalt, is one of very great in- 
terest to geologists—the stratigraphical and chemical evidence 
seeming to be at variance. 
The Rey. E. Hrtn pointed cut the difference between the cases 
when the dyke was simply filled from below, and when the fissure 
formed a channel for the upward passage of the molten matter. 
Mr. Marr referred to the existence of diabase dykes in Bohemia, 
in which fragments of Orthoceratites were found intact. 
Prof. Jupp congratulated the Author on his very valuable contri- 
bution to petrographical science. He pointed out some of the dif- 
ficulties in accepting the theory of the absorption of stratified 
material by igneous rocks. 
The AvurHor called attention to an angular fragment of sandstone 
included in the rock of the Cleveland dyke. Jt did not iena any 
support to the view that absorption of sedimentary rocks had taken 
place. He admitted that certain stratigraphical facts appeared to 
point to an opposite conclusion, and instanced the manner in which 
certain dykes terminate beneath the surface. He considered, how- 
ever, that the balance of evidence at present was against the idea 
of absorption to any appreciable extent. 
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