Prof. T. G. Bonney—Pebbles in the Cambrian at St. Davids. 315 
stance is only present in small quantities, as in fresh-water lakes, 
the vegetable matter is left simply as lignite. 
If we study the details recorded from borings in the deposits 
forming any great delta, we cannot fail to be struck with the corre- 
spondence between these details and those of the case we have been 
considering. The beds of “peat”? so commonly met with generally 
represent, I consider, the deeper-water accumulation of vegetable 
matter I have so‘often referred to. Some, of course, may be true 
soils; but the majority are far more likely to be due to the causes 
above noticed. If this view be accepted as true in the main, then 
it is obvious that we must cease to regard these beds of “peat” as 
evidence of the former presence of dry land at a platform that owes 
its present position to submergence at a later date. They should be 
regarded as simply an integral part of the normal sedimentary 
deposits that had been formed there; the peat representing, not 
shallow water nor subaérial conditions, but simply deposits that had 
been laid down in the ordinary course in water that was com- 
paratively deep. 
We have but to imagine such beds of the submarine “ peat” 
exposed to the necessary conditions of pressure and chemical change, 
and beds of coal would be formed identical in nearly all respects 
with such as had grown, had died, and had been entombed on the 
spot. 
V.—Norte on some Prspies In THE Basat CONGLOMERATE OF 
THE CAMBRIAN AT St. Davips. 
By Pror. T. G. Bonnzy, D.Sc., LL.D., F.R.S., F.G.S. 
ORE than one kind of rock, as we learn from Dr. H. Hicks and 
other writers,' occurs in the conglomerate which forms a well- 
marked base to the Cambrian system at St. Davids. Sometimes the 
pebbles are mainly vein quartz, sometimes felstone predominates, but 
occasionally, as in the neighbourhood of Nun’s Chapel Bay, quartz- 
ites (using the term rather generally) are not uncommon. At one 
place, not far from a quartz-felsite dyke, these are rather large, 
occasionally about a foot in diameter. From this locality, while 
spending a few days at St. Davids in 1882, I brought away speci- 
mens of three of the most marked varieties of quartzite, of which I 
had slices prepared, thinking that as examples of rocks which were 
probably far from modern at the beginning of the Cambrian age, 
their structures might be instructive. In this I was not disappointed, 
and now that I have had many opportunities of comparing them 
with various quartzose rocks, both Paleeozoic and Archean, I think 
a brief description may have some general interest. 
The first, and least remarkable, was broken from a rather angular 
block about a foot in its longest diameter. The rock is a quartzite, 
rather compact or even vitreous in aspect, nearly white, or of a very 
pale pinkish-grey colour. Microscopic examination shows it to be 
composed almost entirely of quartz. This occurs in grains, from 
1 Q.J.G.S. vol. xl. p. 567, id. (Blake) p. 294. 
