The mass called Jebel Ahmar or the Red Mountain near Cairo, whose slopes consist of an immense accumulation of quarry rubbish, is composed of hard brown, reddish and white sandstone and siliceous conglomerate. In many parts it has the characters of a perfect quartzite, and appears at first sight extremely unlike a member of the Tertiary series, newer than the comparatively soft and unaltered Eocene beds on which it rests, apparently in a conformable manner, though its dip to the N.E. is somewhat irregular, and apparently affected by false bedding. The induration of the beds seems to be local, and to be connected with certain fumarole-like openings which have probably been outlets of geysers or hot siliceous springs, contemporaneous with the deposition of the sand. Zittel I believe first gave this explanation, which suggested itself to me before noticing it in his memoir.

In 1863 Professor James Hall described and figured three abdominal segments, with the telson and its appendages, of a Ceratiocaridal Crustacean, characterized by its relatively large size (about 100 mm. long, and from 10 to 15 broad) and by the presence of strong spines on the distal upper edge of each segment [see annexed Plate, Fig. 2]. This form, from the shales of the Hamilton group (Devonian) of Ontario County, N.Y., he referred with doubt to Ceratiocaris, and gave it the specific name “armatus.” At the same time Prof. Hall described and figured some separate caudal spines, from the Genessee Slate, Ontario Co., as C. ? longicaudus, of which his figs. 4, 5 and 6 may be the same as those of C. ? armatus; whilst fig. 7 seems to be two small body-segements and caudal spines of some other Phyllopod. To these Prof. Hall added, in the same plate, the figure of a relatively large Leperditioid carapacevalve, doubtfully referred to Ceratiocaris as C. ? punctatus, from the Hamilton Group, east shore of Cayuga Lake, N.Y.

The history of opinion upon the subject of cleavage seems to be this. Sedgwick had come to the conclusion that cleavage was a condition, “impressed on certain rocks and in certain regions by the operation of some very extensive cause, after the stratified rocks had undergone great displacement,” and he suggested that the cause might be some kind of crystallization. But Dr. Sorby discovered that the intimate structure to which cleavage is due is not crystallization, but a mechanical rearrangement of the particles of the rock: and he produced it artificially by squeezing clay containing flaky particles. Dr. Tyndall did the same thing with different substances, without introducing flaky particles. In either case it was by pressure that the result was obtained. Seeing therefore that pressure could succeed in laboratory experiments, and that cleavage in the field was ordinarily nearly at right angles to the direction in which the action of pressure might have folded the strata, it was natural to conclude that both folds and cleavage had been concomitant effects of such a pressure. And this appears to be the theory now generally adopted; and is of course in opposition to both of Sedgwick's conclusions. For my part I believe that Sedgwick was right in thinking that cleavage was produced by some very extensive cause operating after the rocks had undergone great displacement; while I agree with Sorby and Tyndall in attributing it to a mechanical action, accompanied with pressure. Nevertheless I do not think that this pressure was the same exhibition of force, that originally folded and elevated the rocks, as explained in Part IV. Thus I am in accord with each of these authors in the domain in which his authority stands highest.

The very full and able review of Dr. Sterry Hunt's paper on “The Geological History of Serpentine,”1 gives me an opportunity, of which I have been for some time desirous, of commenting on certain parts of it relating to my investigations of the typical rock which bears that name. In commenting adversely upon these, I must not be supposed to express a difference of opinion in regard to every part of the paper, because there are many relating to the Archæan schists with which I am in general agreement.

That there is a wide-felt want, among field-geologists, of some rapid and sufficiently accurate method of solving such problems as arise in the ordinary course of their work is proved, if proof were necessary, by the summary of the literature bearing on this subject, given in the April Number of this Journal by Mr. Harker, who has certainly carried it to its highest point, for methods more simple than those given by him it is impossible to imagine. There is, however, a method, by which most of these problems can be solved by inspection without recourse to construction or calculation, which I would submit to the notice of geologists in general

Although Rhætic rocks have already been noticed at one or two points in Leicestershire, viz. at Leicester by Mr. W. J. Harrison and between Barrow and Sileby by Mr. Etheridge, the complete sequence of this series has not hitherto been observed in that country. Very recently our attention has been directed to a section at Wigston, near Leicester, which exhibits, not only the whole thickness of these beds, but also clearly shows their relationship to the overlying Lias and underlying Triassic rocks, and which for an inland section must therefore be considered as quite unique in this country.