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KEV. A. W. ROWE ON TEE 



aggregates ; in nos. 47 and 52 the magnetite is in skeleton crystals : 

 the specific gravity of these rocks varies from 2*86 to 2'90. The second 

 group comprises nos. 53 to 60, rocks of a greyish-brown colour and 

 fine-grained ; of these no. 59 is one of the few pieces that I have 

 found in the gravels, and no. 60 is so much altered that it is some- 

 what difficult to distinguish its component crystals ; they are plagio- 

 clase-augite rocks, of a subophitic texture and containing no olivine ; 

 the augite is in almost all cases in granular aggregates and the 

 plagioclase in microliths. The magnetite in some cases is in large 

 plates and skeleton crystals enclosing augite and plagioclase ; they 

 appear to contain a little biotite ; the specific gravity of these rocks 

 varies from 2*81 to 2*93. The specimens in these two groups have a 

 general resemblance to the subophitic dolerites of Central England, 

 some being very suggestive of the Rowley Rag, and others of the 

 Tideswell Dale rocks ; but upon comparing them with the sections 

 which I have made of the Rowley Rag, the Tideswell Dale rock, and 

 the Mount Sorrell dolerite, and with Mr. Airport's sections of the 

 Central England rocks, I could not find any such definite points of 

 resemblance as would enable one to say with any certainty whatever 

 that they are different parts of the same rock. On the other hand, 

 they do not appear to have any speeial points of similarity with the 

 north of England dolerites ; and upon comparing them with some few 

 sections which I have of the dolerites of Southern and Eastern Scot- 

 land and with Dr. A. Geikie's description of these rocks in the Trans- 

 actions of the Royal Society of Edinburgh, I could not discern any- 

 real points of resemblance. They may be found to be identical with 

 some of the Scandinavian dolerites, but they are altogether different 

 from the few specimens of those rocks which were sent me from Sweden. 



The third group of dolerites, nos. 61 to 83, includes some remarkable 

 specimens of plagioclase-augite-olivine rocks of trachytic texture, the 

 magma in some cases being exceedingly vitreous. These are all very 

 black-looking close-grained rocks, the crystals not being discernible 

 with the naked eye, except the olivine : one of these, no. 69, is from 

 the gravel ; but the specimen was so decomposed that it was only from 

 the core of it that a good crystalline section could be obtained. The 

 magma of these rocks is vitreous, the plagioclase generally in 

 minute microliths and, as a rule, not abundant, in some few cases in 

 granular aggregates, but generally in well-formed crystals, some- 

 times porphjTitically developed and of a fairly dark colour ; the 

 olivine usually porphyritic, in some cases remarkably clear and fresh, 

 but occasionally altered, and in a few instances it is in granular 

 aggregates. The magnetite is often in minute rounded grains, as if 

 the section had been powdered with it ; in some cases it partially 

 or completely fills up crystals of olivine, and in a few sections it has a 

 linear arrangement. The specific gravity of these rocks varies from 

 2*90 to 3*02. So far as I have been able to judge, these dolerites 

 have neither any general nor any special likeness to the dolerites of 

 Central England, except perhaps in these two respects, viz. that ia 

 nos. 76, 80, 81, the olivine is in granular aggregates, which, I think, is 

 somewhat unusual, although I believe it occurs in some specimens 



