260 On Orbicular Granite and Sienite* 



mitiou? soils, in the British series of strata. Tl>e Whitby 

 jtrata I have never !)acl an opportunity of seeing, or any 

 oth«r where aluin is manulacturecl ; nor do I reeollect what 

 Mr. William Smith has ascertained, relative to the Whitby 

 and other aluin -shales. 1 he valuable information which 

 ^J^. Winter has already given on this subject, is, as I hope, 

 but the prelude to further details, which would greatly 

 oblige, 



Sir, your obedient servant, 



No. I'J, Upper Crown Street, JOHN FaREY. 



Westminster, April 5, 1810. 



P. S. The perusal of an extract in your last Number 

 (p. 222) , respecting the orbicular blocks of granite of Talavo 

 and Sartene, and the doubts expressed, whether the latter 

 received their present form by the effects of attrition or de- 

 con)position, induce me to state, that in a cursory exami- 

 nation of Charnwood Forest in Leicestershire, in August 

 1S()7, previous to entering on my Derbyshire survey, I 

 found on Mount-Sorrel common, on the north and north- 

 west of the windmill, several isolated blocks of sienite, 

 from one to several feet of solid content each, which ap- 

 peared at first sight like rounded stones, almost half im- 

 bedded in the soil ; but on a closer examination I found 

 them to be perfectly similar in kind to other blocks nearly 

 cubical, which were lying about on the grass, of which 

 blocks seats are made at the doors of many of the houses in 

 Mount- Sorrel town, which most travellers that way must 

 have observed. Seeing reasons for referring the rounding of 

 the blocks in question to decomposition rather than attrition, 

 I attempted, and succeeded in two or three instances, in 

 turning over these blocks, by which it appeared evident to 

 me, that attrition had had no share in giving ihen> this 

 semi-orbicular form ; the bottom in contact with the soil, 

 presenting a perfect face of the cubical form peculiar to 

 these blocks, and no appearance of breaking or other vio- 

 lence : in a further search on this common, I found such 

 a series of these blocks in all stages of their decomposition, 

 as to leave no doubt on my mind on the subject. 



In the progress of my subsequent survey, 1 have found' ^ 

 numerous instances of round masses of granite, of very 

 different species apparently, some very large,' but none of 

 these boulders admitted of any hesitation in referring their 

 form to attrition, or in considering them as the alluvial 

 ruins of very distant regions. One of these granitic boulder* 

 I found in the Buts pasture at Ashover, on the limestone, 

 joiiie in Breiby Park, on the red marie, some on Maccles- 

 field 



