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.

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.

The March number of The Geologist contains, I observe, a notice of the “Upper Ludlow Tilestones,” and the author invites descriptions of their equivalent beds in other districts. Now, so close are the resemblances, lithologically and palæontologically, between these deposits and those of Forfarshire, that they may be regarded as part of one and the same series. I have been induced, therefore, to throw together the following observations upon our northern Scottish system.

The rocks to which I refer occupy a narrow but extended trough-line along the central district of Forfarshire, commencing on the east near Montrose, and terminating at Babruddery and Rossie Den on the west. They trend in a south-westerly direction, across the river Tay, into Fifeshire at Parkhill, Newburgh, and along the northern slope of the Ochils towards Dunning and Tereagles in Perthshire. These tilestones, and the grey and red sandstones with which they are systematically associated, occupy the whole superficies of that well-known and beautiful tract of country which is bounded by the old crystalline rocks of the Grampians on the north, and by the later felspathio Ochil range on the south; and it includes the celebrated geological localities of Cavonylie, Glammis, Forfar, Kinnordie, Clashbennie, Babruddery, and Parkhill.

In one of my last papers on the “Bottom-rocks” I appended a coloured map to a portion of the first dry-land of our mother-earth, a portion of the first division of the land from those waters “which covered the globe,” a fraction of one of those primeval cracks or ridges which then remotely shadowed out our present continents and oceans; and in the little green patches I gave all the traces known of the first beaches and sands which spread around those low and barren tracts in the great region of North America which I selected for an illustration. To this map I hope soon to add, as supplements, others of South America and of Europe. Africa must be left yet a long while ere one dare make the like attempt. To these maps, from time to time, I shall add colour after colour to show the successive deposition of those great rock-formations in which the animals and plants of the successive life-creations of our planet have been entombed; and I hope also to be able to give charts of the teeming oceans during each of those past wonderful ages severally characterised as the stages of progress and development of organic beings.

The beautiful specimen of Phacops caudatus, which we figure in Plate V., has long been in the private collection of Professor Tennant. It is from the Upper Silurian limestone of Dudley, and would be a perfect example but for the exception only of its having the segments of the body somewhat bent inwards, and slightly distorted from their natural positions by pressure. The lateral edges and their segments are unfortunately obscured by being embedded in the matrix, so that they cannot be accurately delineated.

This characteristic species of Trilobite was first noticed by Brunnich, in 1781, under the name of Trilobus caudatus. It was subsequently termed Asaphus caudatus by Brongniart, Dalman, Dr. Buckland, and other writers. Burmeister, however, in his valuable work on the “Organization of Trilobites,” called it Phacops caudatus, which generic determination modern palæontologists have followed.