204 Rev. 0. Fisher — On Faulting, Jointing, and Cleavage. 



Millepore Rock, Cloughton. Leckenby 

 Leckenby 



Fig. 6. Alaria myuriis, Deslongch. 



Collection. 

 J, 7. Alaria arenosa, sp.n. Dogger Sands, Blue "Wyke. 



Collection. 

 M 8. Alaria ? *' Fusus," Bean, MS. Kelloway Eock, Scarborough. 



British Museum. 

 ,, 9, 9a. Turritella opalina, Quenst., var. canina. Dogger, Blue Wyke. 



British Museum. Front view and whorl enlarged. 

 ,, 10, 10«. Twritella opalina, Qnenst. Same horizon and locality. Leckenby 



Collection. Front view and whorl enlarged. 

 ,, 11, ll«. Turritella quadrivittnta, Phillips. Type Specimen. Same 



horizon and locality. York Museum. Back view 



magnified twice, and whorl further enlarged. 

 5j 12. Turritella quadrivittata, Phillips. Dogger Sands, Blue Wyke. 



Leckenby Collection. Front view, magnified twice. 

 ,, 13,13(1. Turritella ? s"^. Dogger,, Blue Wyke. Leckenby Collection. Back 



view, magnified twice, and whorl further enlarged. 



II. 



-On Faulting, Jointing, and Cleavage. 

 By the Rev, 0. Fisher, M.A., F.G.S.i 



PART I. 

 Geometrical Considerations. 



THE following propositions respecting faults apply to strata, which 

 are either horizontal, or which have a uniform dip. If they 

 have a uniform dip, the country, faults and all, may be supposed 

 turned back through the angle of dip, and the strata will become 

 again horizontal. We need then only think of horizontal strata, if 

 we bear in mind that " horizontal " and " vertical " really mean onlj^ 

 parallel and perpendicular to the bedding. This artifice will simplify 

 the subject ; but it does not imply that the faulting took place before 

 the beds were tilted, which may, or may not, have been the case. 



In practice, the strata of a country are tested by means of a trial 

 bore-hole. We will therefore call a straight line drawn perpen- 

 dicular to the bedding a " trial line." 



Fig. 1. 



Fig. 2. 



o =• o o o 



O O O Ci o 



(1.) If a trial line fails to cut a given thickness of beds, then 

 there is a " downcast " or " direct" fault, of vertical throw equal to 

 the thickness of beds that are missed : and the strata are, on the 

 whole, stretched horizontally, and compressed vertically. 



^ The author has had the advantage of the criticisms of A. Harker, Esq., B.A., 

 F.G.S., Demonstrator of Petrology in the Woodwardian Museum, Cambridge, on 

 Pq,rts I. II. III., from whom he has received some important suggestions. 



