TRANSACTIONS OF SECTION C. 687 



often found closely and firmly adherent to the surface, and this coating Las not 

 unfrequently the appearance of the polished surface known as ' siickensides,' which 

 has probably been produced by the great pressure to which they have been sub- 

 jected. The surface, though smooth and often polished as described, does not 

 exhibit lines and scratches, such as those seen on boulders from the glacial drift. 



These erratics range in size from small pebbles to large boulders, Weighino- from 

 100 lbs. to 200 lbs. and upwards. 



The specimens exhibited have been kindly sent by several members of the 

 Manchester Geological Society connected with Lancashire collieries — viz., Mr. 

 George Wild, Mr. James Eadcliffe, Mr. H. A. Woodward, Mr. II. H. Bolton, and 

 others. 



Mr. George AVilds specimens are mainly fiom the Arley mine of Burnley, the 

 lowest seam in the Middle Coal-measures. Though small in size they are interest- 

 ing for the variety they exhibit of white and grey quartzites. Mr'. James Rad- 

 chffe's specimens are fi-om the lloger seam of the Astley pit, Dukinfield, and have 

 been recently described before the London Geological Society (' Q. J. Geol. Soc' 

 vol. xliii. p. 599). Two of these, of the usual grey quartzite, weigli respectively 

 100 lbs. and 156 lbs. 



The Roger seam is upwards of 500 yards above the Arley mine, the recognised 

 base of the Middle Coal-measures of Lancashire. Mr. H. A. Woodward, of the 

 Clifton and Kersley collieries, near Manchester, reporting upon some recent boulders 

 found in the pits, says that they are found in clusters as a rule, but in a foAv cases 

 singly. 



They are common to all seams of this district, but are most plentiful in tlie 

 Trencherbone seam, the C-feet or 9-feet seam of the Wigan district. 



They are found in the coal, in the roof, and sometimes half-embedded in both 

 coal and roof, at depths from surface of 720 and 1,800 feet. 



All the boulders mentioned come from the jMiddle Coal-measures of Lancashire 

 from the Arley mine as the base to the upper part of the Middle series. 



Some interesting boulders have been recently found in the Lower Coal-measures 

 at Bacup. They are from the Gaunister Coal or Mountain mine, upwards of 1,000 

 feet below the Arley. One of these is a granite, which will be referred to later on ; 

 another small one of quartz felsite, similar to rocks of the Lake district ; and another 

 of grit, among the grains of which a considerable amount of iron pyrites is dis- 

 seminated. 



These boulders are by no means confined to the Lancashire coalfield; they 

 have been recorded from the Leicestershire coalfield by Mr. Gresley and by other 

 observers from the North Stafibrdshire, the Forest of Dean, the South Wales, and 

 other of our English coalfields. 



Yet another important fact to bear in mind when considering their distribution 

 is that they are not restricted to England nor to Europe. They are found also in 

 the coal seams of the United States, where the character and the composition of 

 the boulders and their position in the coal seams accord in all respects with those 

 of our own country, and the description given of them by American geologists 

 would very well apply to our own. 



Professor Orton, State Geologist of Ohio, says : ' These boulders, though un- 

 common, are still in the aggregate numerous, and agree in mineralogical characters.' 



References will be found to these Ohio boulders in ' Geology of Ohio,' vol. y. 

 and ' Report of Progress Oliio Geological Survey for 1870.' 



Fragments of three of these Ohio boulders have been kindly sent to me by 

 Professor Orton, and I have had thin sections prepared of them and of some of the 

 Lancashire boulders. These have been submitted to Professor Bonnev, who has 

 most obligingly examined them and remarked upon them. 



Of the Ohio grey quartzite boulders he says they have the same general characters 

 as the Dukinfield boulders, but a little more distinctly cemented by secondary quartz. 

 Summing up, Pixjfessor Bonney says : ' Of these, most of them tell us nothing 

 beyond thefact that they are, no doiibt, Pah-eozoic rocks, and have probably derived 

 their materials from old granitoid rocks. The " granite " specimen is interesting. 

 It is a rock much more ancient than the Carboniferous, and'the rounded inclusions 



