December, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



609 



effect on the strata may be regarded as a criterion as to 

 whether the infilling of a fissure is actually a dyke or no. 

 On the road between Portrush and Port Ballintrae, near 

 Dunluce Castle, one passes what must at one time have 

 been a great crack in the chalk, and this is filled with 

 volcanic materials. But one looks in vain for any signs 

 of metamorphism of the chalk, other than that which 

 occurs throughout the district, and it is doubtful 

 whether this is anything but an agglomerate, that is, a 

 filling-in of volcanic materials, probably brought into 

 the fissure from above. .\s a rule chalk and other 



i<:«. 





Fig. 6.— Weathered bomb-like concretions in tlie cliffs. 



limestones have been changed for some few inches on 

 each side of a dyke into a marble, often highly crystal- 

 line. Sir Archibald Geikie mentions such a case as 

 occurring in Templspatrick Quarry, Antrim, where for 

 some six inches on each side of the igneous rock the 

 chalk has assumed a finely saccharoid conditifin, whilst 

 its organisms have been effaced. Within a foot of the 

 dyke the chalk has assumed its usual character, and the 



Hlg. 7,— Columns at top of cliffs. Between the two central masses 

 was a later volcanic vent. 



microscopic organisms of the chalk are again discover- 

 able. All who know the chalk cliffs of the Antrim 

 coast, such as those, for instance, which occur at the 

 picturesque but neglected lillle fishermen's port of Hal- 

 lintoy, where there is the maximum thickness of about 

 250 feet of chalk, will remember the indurated rocky 

 cliaracter of the chalk, but this occurs far aw ay from any 

 lava lilkd fissures. It is usual to attribute tins indura- 



tion to the baking process caused on the out-pouring of 

 the lower basalts over the plateau. If this be the direct 

 result of the operation it seems strange that the in- 

 cluded fossils remain so apparent as they do; whilst 

 seeing that the contact metamorphism of the chalk ex- 

 tends for but a few inches on each side of a dyke, it 

 is difficult to see in those great thicknesses of indurated 

 chalk beneath the basalt the direct effects of the heat 

 given out from the lava. It was suggested some years 

 ago by Mr. E. R. Sawer that chemical action resulting 

 from the percolation of thermal waters may have played 

 a considerable part in this induration of the chalk where 

 unaffected by dykes, and there is much to be said in 

 support of his contention. It is pointed out that in the 

 Caucasus, the chalk, although it is covered by great 

 sheets of andesitic lavas, still retains its u.sual friable 

 character, whilst on the other hand, in the Crimea, in- 

 durated chalk occurs similar to that at -Antrim, but 

 without any signs of having been affected by igneous 

 rocks- Possibly, by the way, in the suggestion of 

 hydrothermal action we may see the origin of what 

 is known in the south of England as the " chalk rock," 

 on the Holasier planus zone of the chalk. 



Sandstones, when pierced by igneous matter, have 

 been changed into a kind of quartzite, and this has 



Fig. 8.— Basalt rocks off the coast showing dip to the west. 



even assumed ;i columnar structure. .\ similar struc- 

 ture lias sometimes been taken by clay and shale in 

 similar circumstances, instances occurring at Strath, in 

 .Skye, and in Derbyshire, at Tideswell Dale. Geikie 

 mentions that in the .Ayrshire coal-field, a mass of in- 

 tiu.sive basalt ha.s resulted in the coal in contact with 

 it being chruiged into a finely columnar coke. But in 

 all cases the actual distance to which metamorphism 

 has taken place is to be measured in inches only, and 

 contact metamorphism requires a supplementary agency 

 where the effect is found o\er large areas. 



Sectional Ruled Paper Pads. — Messrs. W. and A. K. 

 Johnston. Ltd., have sent us some pads of sectional 

 paper, such as can be used for plotting mathematical 

 lurvcs, as well as for astronomical and other scientific pur- 

 poses. The sheets are of two sizes, S:j inches by loj inches ; 

 and si inches by SJ inches, and are ruled either in niilli- 

 inetres or in inches, and fractions of an inch. 



