This memoir is the result of over thirty-nine years' work among the crinoids of the Scottish Carboniferous limestones. When I began the systematic collection of these fossils few records were noted in any publications dealing with Scottish geology, and in our national museums such as those of Edinburgh and Glasgow there were, and still are, comparatively few species represented. In the official memoirs of the Scottish Geological Survey, dealing with typical Carboniferous counties like Fife and the Lothians, little more than a dozen species are recorded. Some, if not most, of these records are of doubtful value.

The phenomena of the cyclic changes in the human and other mammalian uteri have at all times been a subject arousing interest, inviting speculation, and stimulating investigation. It is therefore somewhat curious that from the plethora of literature concerned in great measure with the histological and physiological interpretations of these phenomena relatively little information is to be obtained concerning the part played by rhythmic variations of the vascular architecture.

In the seaward direction in an estuary there are usually the following main gradients:—

(a) Increase in osmotic pressure (total salt content, especially chlorides).

(b) Increase in calcium and magnesium content.

(c) Increase in alkalinity.

(d) Increase in winter and decrease in summer temperature.

(e) Increase in light penetration.

There are other gradients of less importance. The first three are dependent on salinity. Thus, from the ecological standpoint, the three important physical observations relative to the study of estuarine life are the salinity, temperature, and light (silt content) gradients.

Ecological studies are directed towards the elucidation of two types of problems:

(i) Characteristics of the physical environment relevant to the distribution of specific forms of life.

(ii) The growth of mixed populations and their interrelations in a homogeneous environment or in a physical gradient.

The present study concerns itself especially with the former, and to a less extent with the latter.

Between 1897 and 1903 Ardgour was investigated and surveyed for the Geological Survey by J. S. Grant Wilson. His results were published in the Summaries of Progress of the Geological Survey for 1897, 1898, 1900, and 1903, and were later included in Sheet 53 of the Survey's 1 inch to 1 mile maps and in the Glencoe Memoir. Little additional work had been attempted until 1933 when R. M. Shackelton commenced remapping the area. Shackelton was prevented from completing this work, and the writer supplanted him to continue research on the area from 1934 to 1937 under the direction of Professor C. E. Tilley.

The Ardgour estate comprises a rugged, mountainous tract of Argyllshire north of Loch Linnhe. One large and several smaller masses of epidiorite discovered by Grant Wilson (text-fig. 1) have been intruded into rocks of the Moine Series. Apart from large areas occupied by felspathic granulite and other quartzose types there are also limestones in an amount unusual in the normal Moine Series, some finely banded hornfelses and a zone surrounding the epidiorite masses composed apparently of a felspathised or granitised granulite (indicated by a broken line in text-fig. 1). Pelitic types are important in the western part of the area, and, round Sgurr Dhomhnuill in particular, they have apparently been injected by acid material. This at least is the present view, although the ground has yet to be thoroughly studied. There are a number of lamprophyre and basalt dykes, and some granite, in most places brecciated (with the occasional production of mylonite, e.g. Ben Ba), occurs along the line of the Great Glen Fault. Most of the ground is well exposed, although there may be glacial deposits inland and marine deposits round the coast (not differentiated in text-fig. 1).

The author (1928) of the present communication has already published the results of a field survey of the Lower Old Red Sandstone in Perthshire and Angus, which were linked with those derived by Campbell (1913) from his study of similar and older series of beds in Kincardineshire, to the north-east. For thirty-five miles to the south-west of the R. Tay, no detailed investigation of the sequence or tectonics of the rocks immediately adjacent to the Highland Boundary Fault, separating the Grampians proper from the Central Valley of Scotland, has been undertaken. A comprehensive account of the rocks of this belt in the region around Aberfoyle is available in the paper by Campbell and Jehu (1917).

Since 1912 I have had the intention of re-examining all the available material of palæozoic amphibia, and have done so personally in the case of the Labyrinthodontia, and through my students Drs Bulman, Whittard, and Steen for the Branchiosaurs, and all the small animals from the famous localities of Czechoslovakia; Linton, Ohio; and South Joggins, Nova Scotia. But these researches, although they have included as complete an account as can be made of Hylonomus lyelli, the first animal called a Microsaurian, still left us without a clear conception of that group, if indeed it has any real existence.

Last year, however, Dr Steen was able to show that Microbrachis and Hyloplesion from the Upper Coal Measures of Nýřany were related to Hylonomus and were Adelospondyli.

It therefore became important to examine the well-preserved skeleton, from the Coal Measures of Mazon Creek, Ill., which R. L. Moodie described and restored as a Microsaur. The unexpected results form the paper which follows.

The Bin and Clashindarroch Forests lie some 40 miles to the north-west of Aberdeen. Clashindarroch Forest, the larger of the two, stretches from the Rhynie-Cabrach road in the south almost to the Huntly–Glass road in the north. The Bogie valley in the east forms another rough boundary for the hill mass that the forest occupies. On the west the area marches with the county boundary. The Bin Forest consists of two main sections—the Bin itself to the north-west of Huntly, and the Balloch which lies between Keith and Grange, being partly in Banffshire. Both of these areas are more or less isolated hills.