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HARKER : 
NORWEGIAN RHOMB-PORPHYRIES. 
have been distinguished as such in their Norwegian home. The 
occurrence of rhomb-porphyry boulders at Bridlington, Dimlington, 
and other places on or near our east coast has long been known, but 
nothing more than a cursory notice of them has yet appeared. For 
a full description and comparison we must wait until the several 
types have been more completely and systematically described by 
the Norwegian geologists : the only object of the present notice is 
to point out that the Holderness boulders comprise more than one 
of the types already known in Norway. 
Brogger, in his work on the eruptive rocks of the Christiania 
basin, regards the rhomb-porph3^ries as constituting what he styles 
a "rock-series," that is, an assemblage of types referable to different 
families and exhibiting considerable differences, but having well- 
marked characters in common and occupying similar classificatory 
positions in their several rock-families. Ranging the several types 
with the different plutonic rocks of the district to which they belong, 
he distinguishes : 
Plagioclase-rhomb-porphyry corresponding with Olivine-Gabbro- 
Diabase [Essexite], 
Common rhomb-porphyry corresponding with Laurvikite or 
Augite-Syenite, 
Nepheline-rhomb-porphyry corresponding with Laurdalite or 
Nepheline-Syenite, 
Quartz-rhomb-porphyry corresponding with Nordmarkite or 
Quartz-Syenite. 
The majority of the rhomb-porphyry boulders which have come 
under my notice fall under the second head, but some at once 
separate themselves from the common varieties. A specimen 
received a year ago from Mr. T. Sheppard is an example. It 
shows the grey or partly flesh-coloured porphyritic felspars, with 
the usual rhomb-shaped section and imperfect outline, set in an 
evidently crystalline ground-mass which marks the rock as one of 
the intrusive varieties rather than a lava-flow. The conspicuous 
elements of this ground-mass to the eye are a reddish felspar and 
a dark augite, but a thin slice reveals in addition a noteworthy 
amount of clear quartz. The manner of association of this mineral 
