APPENDIX. 727 



rate of increment for every hundred years. The following- summary, 

 however, of the facts known as to the growth of peat, given by 

 Professor McK. Hughes in a lecture given before the Royal Insti- 

 tution, Friday, March 24, 1876, on ' Geological Measures of Time ' 

 (see Proceedings of the Royal Institution, p. 6), will justify us in 

 setting aside the imperfectly recorded history given above from Mr. 

 Logan's work : 



' He explained the growth of peat, pointing out that there are 

 two kinds of peat ; that which is formed in water, as in mountain 

 tarns or old river-courses, and the peat that grows all over the 

 slopes of moorlands, high and low. The first is partly formed from 

 drifted vegetable matter in the deeper parts, and from the decay of 

 plants that grow on the spot all round the margin, which therefore 

 encroaches rapidly. Here at the outset we meet with a source of error. 

 The rate is very different in these two cases, the quantity of vegetable 

 matter that drifts far in being generally very small. On the hill-sides 

 the growth is to be referred almost entirely to two or three species 

 of moss, and in a smaller degree to the heather and other plants. 

 As the lower part of the mosses sphagnum and hypnum decay away 

 and add to the layer of peat below, the upper part grows on, and 

 so a thick layer of vegetable matter is at length accumulated. 

 Workmen tell us that when they have dug a trench into a peat- 

 moss, if they leave it alone it fills up again, or, as they would say, 

 the peat grows again. This happens when the peat is apt during 

 some seasons to be full of water, so as to become a kind of slush or 

 ooze. It is perfectly clear that the apparent rate of accumulation 

 where such filling in occurs must often be deceptive. A good 

 example of a similar thing happening on a large scale in nature is 

 the case of the Solway Moss, and many other instances as recorded 

 by Lyell. 



' So we see that while the peat is being formed it is subject to all 

 kinds of variations, and when it has been formed it is liable to be 

 soaked with water and run, destroying the value of all evidence 

 to be derived from any observation on its rate of growth else- 

 where.' 



On the other hand, my own excavations in Roman rubbish-pits 

 have furnished me with something of an argument to set against 

 the reported discovery of hives under peat. When excavating in 

 1868 (see Archseologia, xlii. p. 476) a very large pit of that kind at 

 Frilford, I was much struck with the relatively great abundance 

 amongst the various kinds of earthen vessels there represented by 



