Fourth Report of the Committee, consisting of Professor HARKNESS, Prof. PRESTWICH, Prof. HUGHES, Rev. H. W. CROSSKEY, Prof. W. BOYD DAWKINS, Dr. DEANE, Messrs. C. J. WOODWARD, L. C. MIALL, G. H. MORTON, and J. E. LEE, appointed for the purpose of recording the position, height above the sea, lithological characters, size, and origin of the more important of the Erratic Blocks of England and Wales, reporting other matters of interest connected with the same, and taking measures for their preservation. Drawn up by the Rev. H. W. CROSSKEY, Secretary. THE Committee has pursued the same course as during former years. The time for generalization has not yet arrived. There are many erratic blocks scattered over the country as yet unrecorded, and their character and distribution will largely affect any conclusions that may ultimately be reached. The Committee has for its present duty the collection of facts; when its labours have resulted in a complete account of the isolated boulders and groups of boulders of England, Wales, and Ireland, material now unavailable will exist for theoretical discussion, and many important incidents in the history of the glacial epoch will be more accurately determinable. The importance of the work undertaken by the Committee continues to be emphasized by the destruction which is constantly going on. War is waged upon the boulders (which in many cases are our only source of information respecting the epoch to which they belong) by agriculturists, and builders, and road-makers with unceasing energy. They are built into walls, buried in the earth, used as foundation-stones, and often blasted to pieces; their preservation is difficult to secure, on account of their interference with the culture of the land. In a few years it is not too much to say that the evidence of glacial phenomena will in many districts be almost effaced. The Committee directs attention to (1) the distribution of erratic boulders from different centres of ice action; (2) the agencies by which they have been transported; (3) the different periods in the glacial epoch to which they belong; (4) the heights above the sea at which they are found, indicating large changes in physical geology. The schedule of inquiry, indicating the various points of the information required, printed in a former Report, has been issued, and copies may always be had on application to the Secretary of the Committee. DEVONSHIRE. A very remarkable group of boulders has been reported upon by Mr. George Doe, of Great Torrington. It is found in the estate of Rivalton, in the parish of Langtree, Devon, about four miles from Great Torrington. The dimensions of the largest boulder of the group are 13 ft. x 6 ft. x 3 ft. It is subangular in form; but there are no groovings or striations. It rests on clay, close to a small brook, and is about 500 feet above the sea-level. The only legend connected with it is the old story of its having been thrown by the Devil. At the distance of about 25 ft. N.E. is another boulder 3 ft. x 3 ft. x 21 ft. At a distance of 35 yards are six small boulders, cropping out from the ground. At a distance of nearly half a mile are three more, similar to the last mentioned. Near them is a deposit of flints in clay and a gravel-pit. All these blocks except the first are south of the large boulder. These boulders consist of felsite, resembling that in many of the "Elvans." A felsitic Elvan, at Tresavaen, Gwen-nap, Cornwall, cannot be discriminated from them. Possibly, however, a nearer locality may be found. OXFORDSHIRE. Professor Prestwich describes a boulder found last summer, near Oxford, in a bed of subangular flint-gravel (high-level river-gravel), at Wolvercote brick-pit, on the high road from Oxford to Woodstock, at an altitude of about 40 feet above the level of the river Isis. It consisted of a mass of hard saccharoid sandstone of concretionary origin, some portion of it broken away, and the broken edges quite angular; it weighed about three tons. It bore no trace of ice-scratches. There were no fossils to identify the sandstone; but from general characteristics, Professor Prestwich thinks that it is of Tertiary origin. Several smaller boulders, of fromto 2 or 3 ft. cube, more or less worn, were dispersed irregularly through the gravel, which is scarcely at all stratified, and contains no fossils. MIDLAND COUNTIES. Dr. Deane and your Secretary have examined numerous boulders in the neighbourhood of Harborne, to W. and S.W. of Birmingham, between the Hagley and Bristol roads. One hundred and sixty rounded and subangular masses of stone have been examined in this district. Fifty-five of these are clearly traceable to local rocks-Carboniferous, Permian, or Triassic; the remainder are of distant origin. Very few of these travelled boulders are in situ. They have been rolled or dragged off the land into ditches and by roadsides. Some, when the size has been convenient, have been used by the "nailers" of the district for hammering (or rather anvil) purposes. Ninety are of the varieties of felstone so abundant in the Bromsgrove district. About half of these are of small size. Five are of considerable magnitude-5 ft. 6 in. x 5 ft. x from 2 to 3 ft.; the rest are from 2 to 4 ft. in length and breadth, with variable thickness. One of these felstone boulders (near Hole Farm, Moor Street, about two miles east of Hales Owen) is worthy of special notice. Its dimensions are 3 ft. 6 in. x 2 ft. 6 in. x 2 ft.; and it contains in one specimen the three characteristics named in a previous report as occurring separately in the boulders of Bromsgrove. A compact, almost hornstone-like matrix contains distinct included fragments and porphyritic felspar crystals. This specimen, therefore, confirms the view that these felstone boulders, which are so numerous to the west and south of Birmingham, as far as and beyond Bromsgrove, are portions of highly indurated. ash-beds. At Flavell's Farm, California, is one boulder of grey granite 2 ft. by 1 ft. 8 in. by 1 ft. Vein-quartz and quartzite constitute nine small and three large boulders; and one of these, found near Harborne station, contains included brecciated fragments of rock. The size of these quartzite boulders, the largest of which measures 3 ft. x 2 ft. 6 in. × 2 ft., negatives the idea that they have come from the Bunter pebble-beds. The general character of the boulders of this district is similar to that of the Bromsgrove district; but in the presence of granite, quartz, and metamorphic rock resembles the district north and west of Wolverhampton. North and west and south-west of Wolverhampton, however, granite is very much more abundant than in the district west and south-west of Birmingham. The large boulders north and west and south-west of Wolverhampton are, it is probable, chiefly Criffell, or (more sparingly) Wigtonshire granite*; but there is Eskdale granite in the neighbourhood, especially about Bridgnorth. The Welsh felspathic drift covers abundantly the west and south-west of the Midland tableland, while felspathic rocks from the Lake-district accompany the Eskdale granite, and are often mixed with the Criffell granite. The boulders occur in two distinct positions—(1) in the older glacial beds, (2) in the upper clay. LANCASHIRE. Large striated boulders have recently been exposed in the extensive excavations which have been made in the boulder-clay at Bootle, a northern suburb of Liverpool. The site excavated is intended for new docks, and extends along the river Mersey, being reclaimed from shore within the tidal range. Mr. G. H. Morton describes for your Committee the position of these boulders, and gives the following section of the drift deposits which have been exposed continuously over many acres. The thickness of the various beds varies considerably according to position, and the middle sands and gravels often thin out and leave the upper boulder-clay reposing on the lower. The whole of the subdivisions, 1 to 4, repose in succession on the Bunter Sandstone at that part of the section nearest the old coast-line. The Lower Boulder-clay contains a much greater quantity of small stones than the Upper Clay. No large boulders were observed; but as the Lower Clay is not exhibited to any considerable depth, it may possibly contain some. The Middle Sands and Gravels consist of sands which frequently, by the great increase of rounded pebbles, become gravels, resembling those at Preston Junction, Wigan, Gresford, and Colwyn. The Upper Boulder-clay contains comparatively few small smooth stones, but many large boulders two or three feet in diameter. Many of these are striated, and are composed of greenstone, but some are Eskdale granite. These large boulders possibly occur at an average distance of twenty yards from each other. A large mass of compact gypsum, about 4 feet in diameter, was noticed. The sections described are still exposed at the present time, August 1876. * See paper by Mr. Mackintosh, Quart. Journ. Geol. Soc. vol. xxix. p. 358. |