Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/222

 rocks the island must have been situated in a deep sea ; and the fine- grained beds could then have been produced from an admixture of the rock composing the island, or of a rock somewhat similar in character. These rocks are not seen in contact with the island at all places ; but there is evidence to show that they have been faulted downwards at these parts. I am not quite satisfied that there is not a break here in the strata ; for though the strike is nearly the same as in that of the overlying beds, yet there does not appear to be true conformability.

3. Conglomerate composed of quartz pebbles, with a purplish matrix, indicating a shore-deposit. Masses of rock similar to the green beds of the island are also present ; and the whole might easily have been formed out of parts similar to portions of the island now visible. The purplish colour could easily arise out of the green under another state of oxidation of the iron ; for the frequent alterations shown in these lower rocks from purple to green and red, even in the same bed, make this matter of colour of little importance.

4. Greenish micaceous sandstones, with ripple-markings on the surface, and indicating shallow-water or shore-deposits. Worm- burrows and holes are common in these sandstones ; and at present they are the only indications found of the existence of life at this period.

5. Finer-grained red flaggy beds, sometimes, however, of a bright green colour. Here we have plentiful indications of the presence of animal remains. These beds were apparently deposited in moderately shallow water not far from shore. Brachiopods are abundant, as also some small bivalved crustaceans. Some fragments of a trilobite also have been discovered in these beds.

6. A great thickness of purple and green sandstones and grits, with the surface of the beds frequently ripple-marked. These were evidently deposited in shallow water, or formed a sea-beach. The only evidence of animal life found at present in these beds consists of worm-burrows and holes, which occur very generally throughout the whole series.

7. A varying series of beds, at first gritty and of a yellowish colour, with also some fine conglomerate, then greenish and of finer grain, and afterwards red and purple sandstones. The finer beds here, as before, yield the greatest number of fossils and the greatest variety of forms. Between the grit-beds in the first part of this series there are some thin bands of very fine shale, which must have been made up of a muddy deposit, probably washed down by a river ; and on these we have those markings figured in pl. xvi. vol. xxvii. of the Quart. Journ. Geol. Soc. which I have named Protospongia? major. It is really doubtful at present what these are ; and I am sorry the figures do not quite show their true character, as, instead of being simple lines, they should indicate flattened fibres, as described in the same paper, p. 401. Possibly they are impressions of the fibres of sea-weed only ; whilst, on the other hand, there are some facts, such as the thinness of the bands frequently interstratifying very rough grit, to indicate a possibility of their being brought down by a river