78 W. A. E. Ussher — Historical Geology of Cornwall. 



which vary from 60 to 180 acres, Mr. Peacock says that eight 

 carucates would have amounted to 490 aci'es, whilst ' the present 

 dimensions of the Mount, measured from the Ordnance Map, "are 

 found to average 22 x 14 chains; the area therefore is 30-8 acres; 2 

 and it is quite clear that, so far from there being eight carucates of 

 arable land, there can hardly be a single acre capable of being 

 ploughed, because the ground is too steep and rocky." 



Mr. Peacock 3 believes that at the date of this description in the 

 Domesday Book (in the year 1086), St. Michael's Mount was not an 

 island, for the following reasons : Firstly, because neither the 

 Domesday Book nor the Saxon name Michael Stop give any reason 

 for such a conclusion. Secondly, because it is the custom in the 

 Domesday Book, " when a place is an island, to call it so." Of this he 

 gives examples. Thirdly, on account of its then containing at least 

 eight times as much land as at present. 



Of the several remaining competitors for the Ictis of Diodorus, Mr. 

 Peacock disposes as follows : — 



As the Scilly Isles do not lie between Europe and Britain, and as 

 there is a 43-fathom sounding between them and the Land's End, 

 none of them would answer to the description of Ictis. 



As to the Isle of Portland or the Isle of Wight, so accurate an 

 observer as Diodorus would not have failed in distinguishing their 

 position definitely as " near the south coast of Britain, nor are there 

 any grounds for the supposition that the relations of either locality 

 to the mainland were different in Diodorus's time from the present." 



"With respect to the claims of Mont St. Michel, he considers that the 

 space between it and the Continent was the Forest of Scisy and not 

 sea until seven centuries and a half after Diodorus's time. 



As alternatives, Mr. Peacock proposes the Wolf Bock (which would 

 be opposite Britain if a westerly and north-westerly extension of 

 the Cornish coast be conceded) ; the Seven Stones ; or some island 

 now totally lost. He considers, however, that the identification of 

 Ictis is " both impossible and unimportant." 



Mr. Claypole 4 gives an estimate of the uniform rate of depression 

 of Mounts Bay on assuming the identity of St. Michael's Mount 

 with the Ictis of Diodorus and the Ocrinum of Ptolemy. He says : 

 " It must then have been an island as now at high- water only. In 

 the time of Diodorus the isthmus must have been below high-water 

 mark. So depression must be restricted to limits allowing the 

 isthmus to have been below the upper limit of 20-foot tide, 1800 

 years ago, and above its lower limit now : so that it would not have 

 exceeded 6 feet, therefore the rate of depression would be 4 inches 

 per century, which would be 6 feet in 12,600 years." 



Mr. Pengelly, 5 commenting on the evidence furnished by the 

 caverns of Devon, gives the following general note, which may not 

 be out of place here : "In order to obtain the whole, we must add 

 to this part the time represented by the lodgement of the Blue 



1 Peacock, p. 135. 2 lb. p. 114. 3 lb. pp. 112, 113. 



* Proc. Brist. Nat. Soc. 1870, vol. v. p. 35. 

 5 Journ. Royal Instit. Com. for 1873. 



