54 report — 1865. 



tions being taken it would be impossible to place any reliance in the results ; yet 

 it is well known that too often no attention is paid to this subject. 



A series of specimens thus collected are now prepared, and being submitted to 

 chemical examination, whilst at the same time to examine their mineralogical 

 structure, sections have been carefully ground and mounted for the microscope, 

 thus enabling rocks, which to the naked eye presented nothing but a dark, indi- 

 stinct surface, as if composed wholly of but one mineral, to be at once resolved into 

 the various minerals which actually enter into their composition. Their specific 

 gravity was also carefully determined. It would take up too much of the time of 

 the Section, and prove too uninteresting to go over the percentage figures of the 

 analyses already made, or to go into the details of the methods employed in the 

 chemical examination, especially as it is intended that these results should be laid 

 before the Section as soon as the whole of the contemplated series of analyses are 

 concluded, and better enable comparisons to be made between the different rocks. 

 I may only state that rocks have been already analyzed from some seven different 

 localities, and microscopical examinations made of about fifteen localities. Some 

 points, however, have been satisfactorily ascertained, to which attention will be 

 directed in a few words. 



As will be seen from the map of the Ordnance Geological Survey, the bosses of 

 igneous rock which present themselves at the surface are some thirteen in number; 

 the most extensive of them all being the Rowley I [ills, <■< >vering an area of probably 

 about 2i square miles; after which the "Wednesfield and Barrow Hill eruptions 

 come respectively next in extent, whilst the remainder are on a mnch smaller scale. 

 Besides, however, such rocks as are visible on the surface, the extensive mini re- 

 operations for coal have disclosed numerous dykes cutting through the coal-measures 

 and frequently forming large masses, or more or less regular sheets of hard rock, 

 imbedded in the strata. These are generally less compact in appearance, and of a 

 lighter colour than the larger masses, and are known to the miners of the district 

 as " green rock," presenting some resemblance in external appearance to a green- 

 stone, but in reality quite distinct from that rock. A third variety of igneous rock 

 forms small dykes and veins, often very irregular, and altering both the coal and 

 the rocks in contact with it ; it is known to the miners by the appellation of 

 " white horse," and is occasionally called white trap or felspathic trap. 



I have already completed more than one chemical and microscopical analysis of 

 each of these three varieties of igneous rocks which so often have been looked upon 

 as different, and the results are so satisfactory as to leave no doubt but that 

 all these rocks, however dissimilar in their present appearance, are in reality one 

 and the same rock, or rather were originally identical, and in all probability made 

 an eruption from one focus, and more or less contemporaneously. I cannot, howevi r, 

 endorse the opinion which has been expressed, that they are contemporaneous with 

 the deposition of the coal measures, but rather am inclined to look upon them as 

 of later date, and intruded after the consolidation of the same. For this reason 

 also I am disposed to look upon the belt of what is termed basaltic ash, and laid 

 down as such in the latest edition of the maps of the Ordnance Geological Survey, 

 merely as rocks decomposed in situ, in part consisting of decomposed igneous rock, 

 and in part of the decomposed, previously altered sedimentary rocks in contact 

 with same: believing that the present Rowley Hills have been exposed and laid 

 bare by denudation of the strata, which I suppose to have originally covered them 

 when they were an irregular mass of igneous rock imbedded in the strata, similar 

 to what can be seen at Pouk Hill. The apparent height of the Rowley Hills, if we 

 look upon them as a mass of igneous rock, as they until lately have generally been 

 regarded, is quite deceptive ; the recent sinkings and cuttings having demonstrated 

 that the igneous rock is but a superficial cap, at most of inconsiderable depth. 



The Netherton canal tunnel, which has been driven through the very base of the 

 Rowley Hills from one side to the other, has shown that this cap of igneous rock 

 has been erupted through a dyke not more than 8 feet wide, and which was the 

 only one cut through in driving the entire length of the tunnel, and is apparently 

 the only channel or conduit. The terms of basalt, greenstone, trap, white-rock 

 trap, white felspathic rock, and locally, Rowley Rag, white horse, green rock, fee., 

 have all been applied to these igneous rocks without much discrimination, and it is 



