Diagnosis.—Corallum massive and probably nodular. Corallites polygonal, often pentagonal, and, where the walls are not well defined, appear circular. Calices from 2 to 3 mm. in diameter; the width of cœnenchyma separating them varies from ·5 to 2 mm. Septa twenty-four in number, subequal; the trabeculæ are distinct in some and in others fused together. Pali rounded; they occur in three crowns, the primary pali being larger than the others. They are sometimes quite separate from the septa, and sometimes completely fused with the septal ends. Together with the columella they occupy a space equal to one-third of the diameter of the clayx. Columella fairly large, though somewhat irregularly developed. Occasionally it is so small as to appear papilliform, but it is generally clearly fascicular.

The fluctuations which take place from time to time in the lengths of glaciers are extremely interesting to the glaciologist; for there are good reasons for believing that the meteorological conditions which give rise to the lesser oscillations of glaciers are generally of the same character as those which produced the great secular changes of climate which occurred in past ages.

Sedimentary rocks show a variety of minor structures whose origin has been obscure. Among these are the small circular pits and mounds which sometimes mark the surfaces of sedimentary strata. Such of these as cannot be referred to rain-prints or the work of worms are apt to be referred by the geologist to some obscure type of concretion.

This paper attempts a brief summary of the structure of the Northern Pennines for geologists and geographers, especially for those who are interested in the relation of geographical form to geological structure. It is, for the most part, a re-statement, and advances little that is new; but it is thought that the present visit of the Association to the North may be a fitting opportunity to summarize our knowledge of the structure of an interesting region, especially as considerable progress has been made in our detailed knowledge of the Northern Pennines since the visit of the Association to Newcastle in 1889.