The application of the microscope to petrology made it possible to I investigate effectively the history of the foliated rocks and of metamorphism. This was done, as it happens, only a very few years before I began any special study of such rocks, so that the account, of my own work almost corresponds with that of the general progress in a knowledge of them. I was led, after some preliminary efforts, into investigating two distinct problems, each of which, as I soon discovered, presented rather exceptional difficulties. These were the pre-Carboniferous rocks of Charnwood Forest and the serpentines of the Lizard. The problem involved in the one was how far some of them were or had been igneous in origin, lavas, tuffs, and agglomerates, or were stratified rocks, which by pressure and mineral changes had been so altered as to be indistinguishable from some of the former. The other introduced the question of the origin of serpentine, about which in 1873 the utmost uncertainty existed. This, from its associations, led on to investigating the nature and origin of gneisses and schists, so that the history of my own studies during the last forty-five years happens to illustrate. some important aspects of the progress made during that period.

It has been known for some considerable time that the highest beds of the Northumberland and Durham Coalfield lie approximately beneath the town of Sunderland. The great syncline of the Coalmeasures of this area is distinctly accentuated in North-East Durham, so that a secondary basin-like depression is formed, in the centre of which these high beds occur. Beneath Sunderland, -where the top layers also exist, the Carboniferous rocks are concealed by the overlying Permian strata, but at a place called Claxheugh on the Wear, about two miles west of Sunderland, the Coal-measures are exposed for a short distance on both the north and south banks of the river.

In the year 1913 the author formed the intention of carrying out a comprehensive investigation of the mineral composition of the Lower Greensand strata of England, in order to ascertain whether any definite conclusions could be drawn as to the sources of the material and the geographical conditions that existed while the deposits were being formed. A large number of specimens were collected along the out crop from the Wash to the borders of Buckinghamshire and examined by the usual laboratory methods. This work was interrupted by the outbreak of war, and on returning to Cambridge after an absence of nearly four years on Government service circumstances proved to be unfavourable to a continuance of the work on the scale originally contemplated. The district already dealt with forms in itself a fairly well-defined unit, and it was decided to publish an account of the results already attained, in the hope that they may be of service to future workers in this interesting field of petrological and stratigraphical research.

As an illustration of the difficulties encountered in basing the classification on some peculiarity of the Ammonoid suture-line the case of the two families Macroscaphitinæ and Crioceratinæ may again be referred to, the former of lytoceratid, the latter of hoplitid origin. Distinction between these two families was based on the bifid or trifid characters of the first lateral lobe. Hamulina nitida, v. Koenen, which shows very nearly equal-sized suture elements, has the trifid first lateral lobe of the type-species of Hamulina, namely S. dissimilis, d'Orbigny, but the plain shell of the lytoceratid Anahamulina. Hyatt put the latter into his family Macroscaphitidæ, but the former, and also the clearly lytoceratid Pictetia, into Ancyloceratidæ, i.e. even into a different sub-order. But Anahamulina subcylindrica, d'Orbigny, sp., i.e. the type-species itself, has a nearly trifid first lateral lobe, though it is connected through A. Lorioli, Uhlig, sp. (with a sub-bifid first lateral lobe), with typically lytoceratid forms. In ornament and coiling also Hamulina resembles certain lytoceratid forms (compare e.g. the various forms of Macroscaphitinæ figured by Uhlig).

“The Igneous Geology of Carrizo Mountain, Arizona,” by W. B. Emery. Amer. Journ. Sci., vol. xlii, pp. 349–63, 1916.

This region includes various intrusive bodies: sheets, sills, dykes, and a large laccolith of diorite-porphyry. The presence of six volcanic plugs also indicates extrusion, though all flows have been removed by erosion.