longer and broader than they are thick: one or two that I measured were six feet in length, containing from 80 to 90 cubic feet of stone, and must have weighed from four to five tons; others (which had been broken up) appeared to have been of much larger dimensions. The whole of the blocks showed a distinct bedding, which when in situ invariably ranged with the stratification of the drift; and I was therefore convinced that the consolidation had taken place where they occurred. One remarkable point was the isolation of each individual block; for although the masses were placed at a general level, they did not appear to occur as a connected band. There was not even any gradation between the extreme compactness and hardness of the blocks and the loose drift forming a horizontal continuation of their strata, and out of which they were evidently composed.

The power of consolidation did not seem to be related to any particular variety of the drift, as some of the blocks were composed wholly of sand, some entirely of pebble-beds and gravel, and a few of the thicker individuals included alternations of fine sands and pebble-beds in the same block, all alike remarkable for their extreme hardness.

The general aspect of the blocks, although varying much in character and composition, strongly resembled the "Greywethers" or "Druid Sandstones" of Wilts and Berks. Some were quite saccharoid in structure; and others could not be distinguished from compact millstone-grit, except by the presence of fragments of flint; indeed, hand-specimens might be selected to match almost any of the sandstones and conglomerates of the Paleozoic rocks, which they more closely resemble than later formations. A few of the blocks contained comminuted chalk; and as these were invariably softer than the others, it occurred to me that they might be in a more incipient stage of concretion than the saccharoid blocks, which exhibit no trace of separate chalk particles. It is possible that the finely divided chalk first formed the cementing medium, and that on its gradual dissolution the crystalline structure of the blocks has been slowly perfected through the agency of a small quantity of lime in solution. Some of the blocks are so extremely compact that the original sandy agglomeration seems to have given way to an inherent crystalline structure. The water of the well sunk through the drift is strongly chalybeate, and throws down, on standing, a thick sediment of lime and iron; the drift-bed itself, therefore, supplies all the conditions necessary for its consolidation.

On reaching the sand through the Boulder-clay in sinking the well, much "foul air" or carbonic-acid gas was given off; and from this cause the life of one of the well-sinkers was sacrificed. The discharge of gas, apparently from the chalk, still continues; and it may be distinctly heard bubbling up through the water, which stands at a level with the top of the chalk. The solvent power on lime and iron, of carbonic acid in solution, will readily account for the chalybeate character of the water, and suggests an explanation of the means by which the drift was first cemented together: the comminuted chalk, which is largely intermixed with the sand and gravel,

would be gradually dissolved out by the carbonic acid, and the soluble carbonate of lime would form the cementing medium for the residue.

When it is borne in mind that the soluble and insoluble conditions of carbonate of lime are easily interchangeable through different proportions of the acid, the cementing together of Drift containing calcareous matter, by springs charged with carbonic acid, is readily explained; the only difficulty with respect to the blocks in the Coddenham drift is the isolated and unequal way in which the process has acted. In such open porous gravels, water charged with carbonic acid would freely percolate through the entire mass; and it seems difficult to explain the consolidation taking place in well-defined unconnected patches, unless it results from the local discharge of carbonic-acid gas at particular points.

The whole of the concrete masses at Chopping's Hill Farm were readily resolvable into sand and gravel by the action of hydrochloric acid, proving that they were held together by a calcareous cement.

The block before referred to, resting on the Red Crag near Woodbridge, contained no carbonate of lime, but a small quantity of lime in the form of silicate. The following is an analysis by Dr. Voelcker::

Analysis of Saccharoid Block resting on the Red Crag near

A Sarsen Stone from Avebury, Wilts, contained a little free carbonate of lime, but otherwise showed a composition somewhat similar to that of the block from Woodbridge :

Analysis of Sarsen Stone from Avebury, Wiltshire.

The composition of both of these stones indicates the presence of from two to three per cent. of silicate of lime and alumina, which appears to hold the siliceous particles together.

It is probable, as in the case of the concrete masses at Chopping's Hill Farm, that carbonate of lime was the original cementing material, and that lime in solution in contact with the silica, and a small quantity of alumina, would form a thin coat of silicate of lime and alumina round each particle of sand, and agglomerate

them together into a saccharoid mass insoluble in hydrochloric acid.

The beds of gravel including the blocks contain fragments of marine shells, as Turritella, Cardium, Cyprina, &c., examples of which I obtained from a gravel-pit near Hemingstone Church.

Unless it can be proved that the coast Boulder-clay of Norfolk is really older than that occupying the high ground of the eastern counties, the gravel containing the consolidated blocks would appear to be the lowest member of the Boulder-clay series in the east of England.

2. NOTES on some CHEMICAL ANALYSES of VARIEGATED STRATA.
By GEORGE MAW, Esq., F.G.S., F.L.S., &c.

[The publication of this paper is deferred.]
(Abstract.)

THE author gave the results of some analyses for the determination of iron in the light and dark parts of variegated slates, sandstones, and marls, the colour of which is due to oxide of iron, and in which the variegation appears to be disposed independently of mechanical arrangement. The analysis in each case exhibited the fact that the lighter blotches, spots, and stripes contained a smaller proportion of the colouring oxide than the average mass, a proportion which implies an actual difference in the percentage of the metallic iron, and which could not be accounted for by any mere difference in the state of its combination. This shows an actual departure of a part of the colouring oxide out of the colourless patches, and a dispersive process which seemed to be the very reverse of the segregation of nodules of carbonate of lime and carbonate of iron out of a clayey matrix. Among the forms of variegation referred to were:-(1st) that resulting from the segregation of dark blotches out of a lighter matrix, the evenness of colour of which does not appear to have been materially affected by the withdrawal of a part of its colouringmatter; (2nd) that resulting from the segregation of dark blotches out of a lighter ground, each of which is concentrically surrounded by a distinct and well-defined zone lighter than the general ground; (3rd) strata variegated with light blotches containing a smaller proportion of colouring-matter than the general ground, but not arranged concentrically round a darker nucleus; (4th) the variegation of coloured strata with both light and dark blotches, containing respectively a smaller and larger proportion of the colouring oxide than the general ground, but which are not arranged, as in the second case, concentrically with each other.

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