﻿528 Correspondence — Mr. C. CaUmvay. 



be complicated by a local upheaval of somewhat horizontal strata 

 into a curve or arch; that then, while still upheaved and so distended 

 laterally, a subsidence may take place towards the crown only of the 

 arch, letting down the keystone, so to speak, as a ' trough ' fault ; 

 then, on an extension of the same subsidence over a larger area, the 

 arch, being keyed up afresh by the occurrence of the trough fault, 

 can only give way by rupture of the nature of an overlap or reversed 

 fault. These overlaps are sometimes on a considerable scale. Within 

 a few miles of the place whence I write, tliere is a well-defined and 

 proved and, as it happens, easily measured fault of this kind, in 

 which the amount of movement is no less than 101 fathoms mea- 

 sured in the plane of the fault, the amount of throw being seventy- 

 four fathoms vertical, and about sixty-nine fathoms horizontal. The 

 hade of this fault is very nearly the same as Mr, Hebert's experi- 

 mental ones, being 47°. I would also call attention to the fact that 

 the doimivard vertical pressure P (vide his diagram) can in no case 

 exceed the actual simple weight of the mass above the fault, and 

 that in actual nature it is impossible {vide Fig. 2) for the left-hand 

 portion to subside unless there be room for it to subside into. This 

 room can, generally speaking, only be got by the horizontal 

 separation of the masses on both sides of the portion subsiding. It 

 would thus appear probable that all direct faults are of the nature 

 of trough faults, that is to say, that either near or far off there is a 

 somewhat parallel fault with an opposite hade, contemporaneous as 

 to date of occurrence, and that this pair of faults meet sooner or 

 later in depth. I would thus suggest that in the case of direct 

 faults Mr. Hebert should in his inference substitute horizontal 

 tension for vertical pressure (which is a secondary effect), and that 

 the rule should be stated thus : — direct faults are indicative of 

 horizontal tension, reversed faults of horizontal pressure. 



Ston Easton, near Bath. H. E. H. 



PEOF. MANTOVANI AND THE ' MIOLITHIC ' PERIOD. 



Sir, — Prof. Mantovani, in your last issue, proposes the term 

 " Miolithic " for a period intermediate between the Palasolithic 

 and the Neolithic. The term appears to be formed upon the 

 " Miocene " of Lyell, which, of course, does not mean Middle 

 Tertiary. Should the Italian Professor establish his new period, 

 he would more appropriately substitute " Mesolithic " for " Mio- 

 lithic." It is to be presumed he uses his terms in a purely local 

 sense, for his Italian Miolithic age is represented as being con- 

 temporaneous with an age which produced " beautiful vessels of 

 perfect work, resembling those of the ancient Etruscans," and was, 

 therefore, probably post-lithic. The teachers of our science should 

 not forget, for the sake of beginners, that the words " Palseolithic," 

 " Neolithic," etc., represent, not absolute epochs of time, but stages 

 in human development. Chakles Callaway. 



"Wellington, Salop, 



