480 M. B. Medlicott — On Faults in Strata. 



turbance, instead perhaps of four main components of one great 

 phenomenon of compression. 



In the later paper (1864:) Pro£ Hanghton develops his mechanical 

 views more precisely. A number of new observations are tabulated 

 from four localities — Donegal, the Mourne Mountains, Fermanagh, 

 and Cornwall, and compared with those from Waterford. In none 

 of the new regions, except perhaps Cornwall, is the natural grouping 

 of the readings so manifest as in the example from Waterford ; so of 

 course there is more scope for arbitrary selection ; when the bearings 

 range pretty closely from pole to pole, the formation of conjugate 

 systems is a simple process. 



Looking independently at the Donegal observations, the most 

 simple combinations of joints are — a Primary system having a range, 

 of 20°, and a mean bearing of 26° north of east ; a Conjugate Primary 

 having a range of 20°, and a mean bearing of 29° west of north ; and 

 a Secondary system with a range of 6°, and a bearing of 31° east of 

 north. The latter is very nearly the bearing of the A system ; and 

 the two former when divided yield two, corresponding very closely 

 with the systems A and C, and two representing the systems A" and 

 C". The Primary Systems of Donegal are therefore tabulated as 

 (A-A"), (C-C"). It may be remarked that between the .small 

 groups A and A in Donegal, there are observations disregarded, 

 although well within the range of the corresponding systems in 

 "Waterford, and which if included, as one would think they should 

 be, would make the agreement much less remarkable than it is pro- 

 nounced to be. 



In the Mourne region the joints are still more equally distributed 

 from pole to pole ; but six systems, each with a range of only 10°, 

 are readily told off, and lettered according to the nearest groups. of the 

 original set, many observations being omitted. 



The majority of the observations recorded in Fermanagh are 

 readily included in five systems.; having the relation of Primary, 

 Conjugate, and Secondary. All the observations in Cornwall are 

 also amenable to a similar order : the main conjugate system corre- 

 sponding very closely to the system A C of Waterford.^ 



It might seem, from the persistent and somewhat forced manner 

 in which the several systems are throughout ticketed in approximate 

 correlation, that Professor Haughton attached some occult meaning 

 to them, analogous to that pervading the De Beaumont theory : but 

 such is not the case ; the absence of such agreement, except in the 

 A C system in Waterford and Cornwall, is expressly noticed. The 

 object of the uniform lettering is to exhibit the data upon which the 

 learned author bases his theory of Primary, Conjugate, and Secondary 

 Joint-systems, having angular relations constant within narrow limits 

 of variation. Tables xi. and xii. of the paper under notice exhibit 

 these limits as deduced from the five series of observations. The 

 slightly elastic method of selection of the several systems may have 



^ These observations for Cornwall would seem to be very incomplete : in M. De 

 Beaumont's recent work, already referred to, at p. 553, M. Moissenet gives a range of 

 60°, with a mean to E.N.E., for lodes of tin ; a range of 60°, mean a little north of 

 east, for copper lodes ; and a range of 50", mean a little west of north, for lodes of lead. 



