402 



and to have crossed the very ground where the armies of Cyaxares 

 and Alyattes probably met. And if the order of events belonging to 

 the reign of Cyaxares, as related by Herodotus, does not accord so 

 exactly as might be wished with this determination, and cannot be 

 entirely reconciled to their dates, Mr. Baily would attribute the 

 confusion to the want of authentic documents at the time the history 

 was written. 



Although the author has employed in these calculations the secular 

 variations of the moon's mean longitude, mean anomaly, and mean 

 distance from her node, as deduced from the formulae of Laplace, and 

 given in the Tables Astronomiques, he expresses some doubts of the 

 accuracy of these results ; and his doubts are founded upon an eclipse 

 recorded by Diodorus to have happened during the voyage of Aga- 

 thocles from Syracuse to invade Africa, in the year 3 10 B.C., in 

 which, when computed according to the present tables, the path of 

 the moon's shadow appears to have passed so much more south than 

 Agathocles can be supposed to have been at that time, that the la- 

 titude of the moon would require to be at least 3 greater than our 

 present tables make it. 



These observations (if correct) would show the necessity of some 

 alteration of the secular variation of the moon's mean distance from 

 her node ; but this hypothesis, Mr. Baily observes, could not be re- 

 conciled with the eclipse mentioned by Herodotus ; for by means of 

 a corresponding correction, the eclipse of 610 would be found not 

 to be total to any part of Asia Minor ; and there is no other that 

 could possibly be central and total within the utmost limits that are 

 reconcileable Avith any received systems of chronology. 



An Account of the great Derbyshire Denudation. By Mr. J. Farey, Sen. 

 In a Letter to the Right Hon. Sir Joseph Banks, Bart. K.B. P.R.S. 

 Read March 21, 1811. [Phil. Trans. I8ll,p. 242.] 



It is now well known, says Mr. Farey, to many observers in geo- 

 logy, that the clay strata on which the metropolis is situated, extend 

 north-eastward through Essex, Suffolk, and Norfolk, and are incum- 

 bent on the great chalk stratum, which reaches from the Isle of 

 Wight to Flamboro'-head ; and that these, as well as many subjacent 

 strata that are known, dip in general to the south-east, and basset 

 out, or appear at the surface in succession, to any one travelling to- 

 ward the N.W., until he has passed certain strata of lias, clay, and 

 sand. Beneath these, says the author, are found marks of an im- 

 mense stratum of red marl, which seems (to him) to have extended 

 over all the remainder of the British islands. In this stratum are 

 contained local strata of gypsum, rock salt, sand, micaceous grit- 

 stone, &c. : to this stratum also, according to the author, belong the 

 great nodules of slate, green stone, sienite, basalt, &c. that form 

 hills or mountains, intersected by mineral veins, in the western parts 

 of the kingdom. In many parts, however, the red marl itself is no 

 longer found ; but instead of it various strata, subjacent to it, have 



