rOL. LXXXI.] PHILOSOPHICAL TRANSACTIONS. 75 



Chalk found in a new place. — ^There is a great deal of chalky ground in the 

 southern part of England; I think it begins at the sea in Devonshire, and one 

 vein of it runs all along the southern counties to Dover. Another vein parts off 

 from that about Reading in Berkshire, goes by Dunstable, BaUlock, and Gog- 

 magog-hills, and so on to the sea in Norfolk; the whole crossing the kingdom 

 in a Y. Along these 2 districts it is almost all chalk to a great depth in the 

 ground; but out of them chalk is seldom found. I believe it may be met with 

 in many places in the countries between these 1 districts, and sometimes deep in 

 the ground, where it does not come up to the surface; but beyond the northern 

 limits of them, which are at Wantage in Berkshire, and over the river from 

 Shillingford in Oxfordshire, and at Maddingley by Cambridge, chalk is hardly 

 any where to be found; no where in any considerable quantity, unless it be much 

 farther north, in the wolds of Yorkshire, beyond Pocklington toward Scarborough. 

 I did not know till lately that we had any chalk nearer us than Maddingley ; 

 but several years ago, the people of Ridlington in Rutland, digging for stone to 

 mend the roads, met with a bed of chalk ; at which they were much surprized, 

 and did not know what it was, having never seen a chalk pit before. After I had 

 heard of it, I went to examine the place,, and found it a regular chalk pit, with 

 rows of flints lying in it as is usual in the south of England. The chalk is not 

 soft like that written with, but very much like that they dig about Baldock ; nor 

 are the flints so black as those in the south of England, but veined, of a light 

 coloured flint, and white, some parts much mixed with chalk ; and are broken, 

 not whole ones. They may have dug the pit 6 yards long and 2 deep ; but how 

 far the chalk reaches I do not know. The ground about it has plainly been for- 

 merly dug, perhaps 30 yards square, but completely turfed over again, with the 

 same strong turf as the rest of the close, which is rich pasture land, and feeds 

 oxen for Smithfield market, not like the short grass on the chalky downs. 



Riding last autumn along the turnpike-road near Stukeley in Huntingdonshire, 

 I saw a little patch of chalk, a few yards long, in a bank which had been dug 

 away by the road side ; so that though we did not know there was any chalk at 

 all in this country, and there certainly is very little, yet here are now 2 places 

 where it has been met with. 



XIX. Description of a Simple Micrometer for Measuring Small Angles with 

 the Telescope. By Mr. T. Cavallo, F. R. S. p. 283. 



The various telescopical micrometers, or machines which have been con- 

 structed for the measurement of small angles, may be divided into 2 classes ; 

 namely, those which have not, and those which have, some movement among 

 their parts. The micrometers of the former sort consist mostly of fine wires, 



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