A large portion of the last number of the Quarterly Journal of the Geological Society (February Ist) is justly devoted to the important subject of the Laurentian or oldest known stratified rocks, the elaboration and naming of which in North America were, it is well known, accomplished by Sir William Logan and his associates. On this occasion a memoir by that eminent geologist naturally leads the way, whilst, in the subsequent articles, the nature and structure of the Eozoon Canadense, which has been found in these rocks, are ably developed by Drs. Dawson, Carpenter, and Sterry Hunt.

In the month of May, 1861, there occurred a curious subsidence of the soil in a field on the ‘Malting Farm’ at Lexden in Essex. The cavity thus produced was about twenty-five yards in circumference, of an elliptical form, and about twenty feet in depth, with the sides slightly overhanging. The subsidence took place quite suddenly; some workmen, who were in the field in the forenoon, finding the pit fresh formed on their return from dinner. The ground in which the pit is situated consists of a slightly rising bank of valley-gravel, and is about fifty yards to the south of the little River Colne, which runs past the spot, and gives its name to the ancient town of Colchester. The surface of the field cannot be more than five or six feet above the stream when full.

The Suffolk Crags.—There are few deposits in this country which form so admirable a field for study as the Crags of Suffolk. Unique as to age, the sole representatives in England of the great Pliocene deposits of Europe, it becomes a matter of very high interest to identify them in any way with particular strata in other countries. The lowest of these Crags occurs in small patches over an area of about eighty square miles, and consists of either loose or compact light-coloured sand, alternating with bands of Polyzoa, which sometimes form a kind of limestone. From this Crag 299 species of Mollusca have been obtained: of these, 148 are extinct, 151 are still living. This so-called ‘Coralline Crag’ lies on London Clay, and is seldom more than 20 feet in thickness. The ‘Red Crag,’ so called from its iron-stained appearance, is an irregularly stratified deposit, composed of rather coarse sand and fragments of shells, abounding also in more perfect remains, but very rarely affording the valves of Conchifera, opposed or in sitû. It extends over a larger area than the Coralline Crag, abont 200 square miles, part of which is in Essex. The Red Crag, rarely exceeding 20 feet in thickness, in most localities rests on the London Clay, the Lower Crag having probably been denuded: it is occasionally, however, found resting on the latter. At the base of both Crags, when resting on the London Clay, a deposit of rounded concretionary nodules, derived from and containing the fossils of the London Clay, is found, and is worked for the nodules, which in great part consist of phosphate of lime, and are manufactured into manure. Associated with these nodules, are teeth of Mastodon, Rhinoceros, and other Mammals,† which have been derived perhaps from earlier Pliocene, perhaps from Miocene strata, and are similar, in some respects, to those obtained at Eppelsheim in Germany. In addition to these, there are the remains of large Cetacea, much worn and rolled, as well as the teeth of the large Carcharodon and Oxryrhina. These are probably the remains of a former Pliocene deposit, broken up like the Miocene beds at the beginning of the Crag era. Similar vertebrate fossils and phosphatic nodules are also dispersed at intervals in the higher strata of the Red Crag. Their occurrence here has led to much confusion, since they have been, and still are by many, regarded as indigenous to the Crag.

The Carboniferous rocks of Shropshire possess several peculiar features; and no member of the series shows these in a greater degree than the Millstone-grit, as seen on Sweeney Mountain, near Oswestry. Before discussing these features, it will not be amiss to detail briefly the character of this rock in other localities. It varies considerably in different places. For instance, in the Forest of Dean, it is a hard intractable rock. Such it is also in Glamorgan and Monmouthshire, where it is often seen in place under the Coal-measures, or in boulders on the hillsides. Varteg Hill, near Pontypool, is a most characteristic spot for it; that hillside being covered with masses of grit, of all sizes and shapes. These masses arenot unfrequently wholly made up of water-worn quartz-pebbles, occasionally as large as a hen's egg, in a cement of sand and decomposed felspar. And although hundreds of houses, with their garden-walls, have been built of them, yet considerable areas of these boulders remain. Very large blocks of this rock may be seen on the southern flanks of the Black Mountains, Caermarthenshire, above the village of Cross-Inn. The Millstone-grit of the South-Welsh Coal-field, which goes by the name of ‘Farewell Rock’— from the fact that the miner on striking it bids farewell to coal, possesses the valuable property of being able to resist successfully for a length of time the action of most intense heat, and for this reason the ‘hearths’ of iron-furnaces are constructed of it.

I have for some years had serious doubts as to the correctness of the Map of the Geological Survey so for as it relatesto the supposed presence of Millstone-grit in the northern portion of the Bristol Coal-field in the neighbourhood of Kingswood Hill; and in a foot-note to a most valuable lecture delivered by my friend Mr. Robert Etheridge, F.G.S. (of the RoyalSchool of Mines) at the Bristol Mining School in 1857, and published in a volume of Lectures issued by that Institution, Ihad, so long ago as that year, expressed doubts as to the existence of Millstone-grit at the surface near kingswood. Sincethen I have had much greater opportunities of investigating the matter, having taken, with my partners, a large tract of mineral property in that district; and the results of those investigations thoroughly confirm the doubts I had previously entertained, and in fact fully satisfy my mind that what is shown as Millstone-grit on the Government Geological Map, as also on the valuable map lately published by Mr. William Sanders, F.R.S., of Bristol, is really nothing more than one of thesandstones (the ‘Holmes Rock’) so common in the Coal-measures proper, and developed on a grand scale in the Pennant-grit dividing the Upper and Lower Coal-series of all the South-western Coal-fields.