Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/47

Rh Stigmarian rootlets in the underclay. Along the strike of the strata there is, at Carribou Island, a thicker coal-seam. Some of the shales contain concretions of limestone which sometimes form a nearly continuous bed; and analyses show that some of the limestones are highly magnesian. These are overlain by a great mass of red and grey sandstones, chiefly red (group 4), which, in their turn, are covered without apparent unconformability by Triassic strata. Dr. Dawson thinks that the strata of the section bear such strong points of resemblance to parts of the European Permian, both in their mineral character and organic remains, that they may be fairly termed Permo-Carboniferous.

The Permian strata are sometimes divided into upper, middle, and lower groups, and sometimes into upper and lower only. In my grouping I have, as will be seen, adopted the tripartite division of the strata. This threefold division is, I think, more true to nature. For while each of the groups 2, 3, and 4 does, in some of the sections, bear resemblances to certain portions of the other groups in other sections, yet, taking the sections altogether and looking at them comprehensively, each group has one or more characteristic features by which it may be distinguished from the others.

Thus the lowest division, group 2, is characterized by the prevalence of conglomerates and breccias, by the preponderance of grey over red sandstones, by the large proportion of the fragments of Cambrian and Silurian rocks in its breccias, by the greenish colour of many of those breccias, as well as by the plant-remains which have been found in most of the sections, and which (in sections 7, 8, 17, 19, 20, as well as in Russian sections corresponding to section 1) have been numerous enough to form thin coals. By these features this group may be distinguished from the sandstones and marls of group 4.

Group 3 is well marked by the presence of calcareous matter, which, usually mixed with magnesia, is more or less interstratified with white, red, and variegated marls, the calcareous matter being most abundant in the north-eastern counties of England. In none of the sections of any thickness are red sandstones and trappean-like breccias present in any force. This group is also characterized, in sections of any thickness, by the presence of shales with plant-remains.

Group 4 is distinguished by the prevailing dull red colour of its sandstones and marls, together with the massiveness of the former and the thinness of the latter, by the infrequency of its breccias and their dissimilarity to the prevailing character of those of group 2, and also by the great dearth of carbonaceous matter and the rarity of plant-remains, although, occasionally, solitary specimens of the latter are found which show a relationship, more or less remote, existing between this and the groups below.

If now we fix our attention on the Ifton section, 11, and compare it with recognized Permian sections on either side of it, we shall see how strikingly in each group it resembles them and possesses their characteristic features.

We see how in group 1 it has a series of upper coal-measures