Persons in general take as the type or representative of chalk the material which mechanics employ for tracing out rough lines and figures. It is a substance of a bright white colour, somewhat yielding to the touch, and capable of being very easily abraded or rubbed down.

But the geologist gives a much wider interpretation to the term, not limiting it by these few characteristics; and, accordingly, he includes under the same title many strata which would hardly be so grouped together by the uninitiated.

For instance, there is at the base of the upper portion of the cretaceous system a certain hard, often pebbly, and highly coloured band, which, notwithstanding its great departure from the popular type, is nevertheless styled in geological language the “Red Chalk.” This stratum, the subject of the present paper, nowhere forms a mass of any great thickness or extent; perhaps if thirty feet be taken as its maximum of thickness, four feet as its minimum, and one hundred miles as its utmost extent in length, the truth will be arrived at. It may be said, also, to be peculiar to England, for the Scaglia, or Red Chalk of the Italians, has little in common with that of our country. The two differ widely in appearance, in situation, and in fossils.

In my last communication, I endeavoured to lay before the reader all the more important facts, already acquired, relative to the genera and sub-genera that are provided with spiral appendages for the support of the oral arms; and at the same time I referred to several points which still required to be elucidated and explained before the subject could be considered to have been satisfactorily studied.

For the Vegetable Kingdom it is impossible to give any list composed with the same degree of elaboration as has been attained in the classification of animals. Modern plants are, it is true, as well known and as correctly grouped as modern animal life-forms; but our knowledge of fossil botany is not at all equal to our knowledge of fossil animals. The most minute divisions as well as the most important of botanical classifications are dependent upon the more fully developed and most perishable parts of vegetable organisms—the flowers and the fruits or seeds. Of these the former, the most essential of all, have rarely indeed, if ever, been preserved. One or two doubtful instances have been stated; but these have been by others disputed as being only incipient buds or leaflets, or as accidental appearances, and the investigator of the extinct forms of the vegetable creations of past geological ages has, at the best, to infer from the remains of leaves, branches, or stems, usually more or less decayed, the probable class to which the originals—often, indeed generally, of very different structures and organic characters from his existing types—belong. Not uncommonly, indeed, his only guides are vague and indefinite resemblances of form. Still, however, if it be essential for the attainment of a knowledge of the exact concatenation of past events in the succession of organic life on our planet, it is equally as important to note whether plants have been progressive in their development, as to determine this point in relation to the animal-kingdom.

As One carried beyond his depth for the first time into the waters of ocean, and struggling shorewards, touches but now and then the yellow sands, with every heaving wave again to be set afloat, feels a delight when he plants his foot solidly on the sands, and wades through shallower water to the shore, so do we after our almost footless path through the wide waste of water of the first age, hail with delight our firmer footing on the spreading shores of this next great geological period.

Much has been written on the geology of Scotland, and perhaps no country has given birth to a larger proportion of eminent inquirers. The names of Hutton, Playfair, Murchison, and Lyell will ever be remembered among those of the great Scotchmen, who by their acquirements, genius, and perseverance, have so materially contributed to elevate the science of Geology to the rank it now holds among all men of learning.

Much has, however, still to be achieved before the geological and palæontological details connected with our country will have been completely worked out, and many zealous inquirers must be summoned to the field; some will do much, others little; but every accurate observation is so much gain, and will tend towards the complete elucidation of the subject, as well as help to form a basis upon which great minds may found with safety their general views and appreciations. I therefore hailed with much hope and delight the foundation of a Geological Society in Glasgow, which originated in May, 1858, with about a dozen young men, who wished to gain knowledge of the geological phenomena in the neighbourhood of their great city, under the guidance of an experienced and practical geologist; and thus, owing to the active co-operation and direction of Mr. J. P. Fraser, and that of some of its founders, the Society has already done some good work, and increased its numbers to about one hundred.

It is now several years since I first became convinced that a diligent study of the various structures produced by the action of the currents present during the formation of stratified rocks would lead to the knowledge of many very valuable and remarkable facts in connexion with physical geology aud ancient physical geography. Since then I have never willingly lost any opportunity of determining the direction and character of the currents present during the deposition of rocks of every age, and of accumulating information on every kind of subject that could throw light upon the inquiry. I must now have, in my note-books, not less than twenty thousand recorded observations, many of which I have not been able to make use of hitherto, for want of sufficient points of comparison; and, although I am most willing to admit that the subject is quite in its infancy, and that I am a mere student of nature, ready to modify my own opinions or to adopt others which would explain the facts in a more satisfactory manner, yet some of the facts are so definite and distinct, and I have verified them in so many localities, over sufficiently extensive districts, as to warrant the formation of definite conclusions. We all protest against theories without facts; but to accumulate a great number of facts without attempting such explanations as would unite them into a complete and consistent whole would be not less unphilosophical.

How sweet the communing with oneself; the thoughts that rise and flee; the dreams of solitude, away from the busy hum of men—quiet—alone with God, thinking of His wonders and His powers, the beauty and skillfulness of His works. As late at night I sat at my open study-window gazing over the forest of roofs and chimneys of the sleeping city, with its towers and church-spires pointing to the holy heavens and star-lit sky, for the first time I heard the great bell of Westminster toll out the midnight hour—sonorous, solemn, slow, as if clinging with throbbing pulse and quivering frame to Time's flowing garments to arrest him in his sturdy march. Solemn and slow the changing hours of past creations have passed away, with no “Big Ben” to mark their passage; but solemn and slow has Time himself impressed his footsteps on the yielding sands of earth, and left us his own record of his onward course.

In the definition which I have given, a mineral is described as a body possessed of a definite chemical composition and a regular physical form,—meaning by the latter particularly crystalline structure. But, while the crystalline relations of each species only vary within the narrowest limits, the chemical composition has a much wider latitude. Many individuals of the same mineral species are found, by analysis, to differ most widely in their chemical components, while the crystalline form is quite unaltered. Now, although we are as yet unable to trace the relation between the form of a mineral and its composition, there can still be little doubt that some such relation does exist, regulated by laws yet to be discovered; consequently, when we find the same mineral species differing widely in chemical proportions, we recognise a departùre from regular although unknown laws, and seek for a cause. This we find in the doctrine of Isomorphism. This, simply stated, in the capability of two or more substances, of analogous chemical constitution, to crystallize in similar forms.

All rocks are necessarily composed of minerals,—that is, of certain “substances which, wherever found, present respectively nearly the same forms and physical characters, and are generally composed of nearly the same chemical constituents.” A rock may consist of one single mineral, in which case it is called a simple rock; or it may be made up of an aggregation of several different minerals, when it is called a mixed rock. Crystalline limestone, which consists exclusively of one mineral, calcite, may be given as a familiar example of a simple rock, and granite, made up of an intimate aggregation of three distinct minerals, felspar, quartz, and mica, of a mixed rock.

Many of the common things that occur to us in our walks and rides near home, and which occasionally are noted in our memorandum-books on account of the clearness of their features, or for the sake of some occasional peculiarities in the details observable in them, may not only often prove as useful exemplifications of natural processes and phenomena as facts and instances brought from any distant part of the world, but may bear repeated description and fresh demonstration for the sake of geological enquirers, such as many of the correspondents of The Geologist must necessarily be.

These veins penetrate the crystalline schists, particularly the gneiss, in those localities where the latter are largely penetrated by porphyry. They also generally penetrate the porphyry; only a few exceptions from this rule serving to show that the porphyry-eruptions continued into the period of the formation of the ore-veins. These veins form three or four principal groups, according to their direction, which groups in general differ both in age and in contents. Still, all veins by no means show similar directions in connection with similar contents, or the converse, only these predominant characteristics often coincide. Veins of distinctive contents are almost as much confined to certain localities as they are characteristic of definite directions. According to the contents we can distinguish three or four paragenetic combinations of different ages, but which often extend into one another in such a manner that one fissure sometimes contains the products of two or three of these different periods.

There is a close resemblanoe between the fossil contents of the “Upper Ludlow Tilestones,” as described by Mr. Roberts, of Kidderminster, in the last number of The Geologist, and those of certain strata developed in this neighbourhood. The rocks of the southern districts of Forfarshire have been described by Fleming and Miller, and their fossils have attracted the attention of the scientific world. I am acquainted with sections in the north-eastern division, an account of which has not yet appeared in print, and it may be of interest to indicate their organisms.

Texture of Ore-Veins.—The varying texture of ore-veins referred to towards the end of Prof. Cotta's memoir may not be intelligible without a short explanation. We find that the two extreme textures of veins may be classed as (1) a compact texture, and (2) a banded or layer-like texture, both of these of course having many varieties, and passing into each other. The first is often characterized by a breccia-texture, that is by containing fragmenta—often very numerous—of the neighbouring rock. The figure below shows an extreme case of this breccia-vein; and also the peculiar manner in which these fragments are usually surrounded by some crystallized mineral, marked by the axes of the crystals all radiating as if from a centre.

I propose, from time to time, in the pages of this magazine, to bring before geologists and geological students translations or abstracts of some of the most authoritative memoirs of foreign geologists on the subject of mineral veins and metalliferous deposits.

Notwithstanding the great commercial value of the metallic mines of the United Kingdom, the subject of mineral veins and metalliferous deposits has not, of late years, occupied the serious attention of many men of recognized scientific position in this country: the late Sir Henry de la Beche, Mr. W. Jory Henwood, and Mr. Warington Smyth are those best known. The strong distaste which undoubtedly exists to inquiries in this field of geology is due to many causes which it would be out of place to discuss here. I may nevertheless be permitted to say that, however just this feeling may have been in its origin, a continued shrinking from all attempts to grapple with the difficulties which admittedly beset this subject is likely to retard the progress of some of the most important branches of chemical and physical geology. The successful solution of many obscure problems can only be hoped for from a long, patient, and accurate examination of the never-ceasing processes of nature working deep in the recesses of the earth, and which are only open to observation in those wonderful excavations which, by the patient toil of years upon years, have been made accessible to us in our mining districts.

The Tilestone passage-beds between the Upper Ludlow rocks and those cornstones, now established as the natural base of the Old Red Sandstone, are, from the interesting character of their animal contents, attracting the greatest interest. I think it would be of value if the pages of the Geologist were open to detailed descriptions of the lithological character and fossils of these “Tilestones,” as exposed in different parts of Shropshire, Worcestershire, and Herefordshire. A comparison may thus be instituted which would greatly aid our comprehension of them.

During the last few years, the native iron-making resources of South Wales have received considerable assistance from the re-discovery and working of some very remarkable deposits of hæmatite in the county of Glamorganshire. I propose in the present article to describe two of the most important, perhaps, of those veins of ore, which are found in the districts of Llantrissant and Llanharry, near Cowbridge, and at Newton Nottage, near Bridgend;—the iron-ore in the latter locality being associated with a very large and curious deposit of manganese, chiefly psilomelane. Prefatory to this description, it may not be out of place to give a few remarks on the physical geology of the surrounding country, inasmuch as this district possesses ample materials to engage the attentive and careful examination of the geologist, particularly in relation to the origin of the mineral deposits in question. The exploitation of these hæmatite-mines will have the effect, commercially, of giving a great development and increased prosperity to the iron-manufacture in the district south of Cardiff; while, as a social result, their being worked will probably bring back to a population, at present agricultural, the mining and metallurgical occupations of the ancient fore-dwellers on the soil, and, what is most desirable, give constant occupation to a very large number of the working classes.

As we have already had occasion to observe, in our monograph published by the Palæontographical Society, the species belonging to this genus were not specifically numerous during the Carboniferous period, and, as far as our observations will conduct us, were characterized by the presence of short simple loops, as may be seen in lignograph fig 1.

The family Terebratulidæ comprises many genera and sub-genera; but these do not all appear to possess an equal value or importance, and time alone will decide how far we are justified in certain of the divisions that have been proposed. Professors M'Coy and King are of opinion that Palæozoic Terebratulæ such as T. hastata, T. sacculus, and T. vesicularis, should be separated from Terebratula proper (such as T. vitrea, T. carnea, and T. biplicata) on account of certain peculiarities, or differences, and have respectively proposed Seminula and Epithyris, Phillips, as generic denominations for their reception.