366 Prof. J. F. Blake — Recent Papers on Faults. 



passed through the greater number of changes appears to be the less 

 altered. If this hypothesis is rejected, we must regard the schist 

 either as a normal part of the Primrose Hill group, or a new forma- 

 tion. If the latter supposition be accepted, the number of Archfean 

 formations in Shropshire is raised to three, viz. : — 1. The Primrose 

 Hill gneiss. 2. The Rushton schist, 3. The Wrekin volcanic group. 

 A geologist with a genius for speculation might conclude that we 

 have in this small area the representatives of three of the great 

 Archaean systems of North America — the Laurentian, the Montalban, 

 and the Keweenian. I would not contradict him,, but I would 

 respectfully hesitate. 



YIII. — Criticisms on Eeoent Papers about Faults. 



By Prof. J. F. Blake, M.A., F.G.S. 



N recent Numbers of the Geological Magazine ^ has appeared 

 a paper by the Eev. 0. Fisher, " On Faults, Jointing, and 

 Cleavage," which, it seems to me, should not be left to stand un- 

 challenged. It is one of those in which mathematical symbols are 

 made to do duty for arguments. Some idea is started, a few Ws 

 and P's are scattered about, an equation is written down, it leads to 

 nothing, and then the conclusion is triumphantly reached. Some- 

 times, however, there is no conclusion at all ; but statements come in 

 incidentally which will hereafter be quoted with the introduction 

 " I have shown." Surely there must be many geological birds too 

 old to be caught by such chaff; but the "Magazine " is also for the 

 nestlings. Such papers, too, are otherwise harmful, for the wide- 

 awake soon learn that credit may be gained by work unfinished, and 

 speculations that are crude, and they are tempted so to seek it rather 

 than by harder labour. So goes our science down and loses caste. 



I trust, therefore, that the author will excuse me if I run full tilt 

 at his production, and if he can return the stroke, and hold his 

 ground, all the better for the spectators. 



Part I. deals with "geometrical considerations." In the very- 

 first paragraph we are told to confound " vertical " with " perpen- 

 dicular to the bedding," and are restricted to faults in strata with a 

 uniform dip. This is very like the play of Hamlet without the 

 Prince of Denmark. Then we are told that in direct faulting the 

 beds on the whole are compressed vertically. This is only the case 

 in the part where the fault is a common boundary, but " on the 

 whole" every dislocation requires greater space in all directions — as 

 may easily be seen by drawing a diagram of a dislocated brick. 



There is no particular harm in § 1 and § 2, and the results are 

 not again referred to. They are simply a few elementary exercises 

 on the addition and subtraction of throws. 



In Part II. we are supposed to have " The Mechanics of Faulting 

 and Jointing." It starts off with the statement that " direct faulting 

 is in many instances the consequence of settlement when the strata 

 contract through solidification." I doubt if it is ever due to this 



1 Geol. Mag. 1884, May No. pp. 204-213, and June No. pp. 266-276. 



