On the Geology of t1te Lake District. 4G5 



faults is evidently pre-Carboniferous. The Lune-valley faults are a 

 great sot (there are, at least, four seen in section) connecting tlie 

 Craven and Penine faults, and as those are of various downthrow 

 and age, so these connecting faults, though by direction to be re- 

 ferred to the N. and S. system, are, in all probability, of various 

 downthrow and age. In all these great sets of faults it will be 

 found, the rule, and not " a rare phenomenon, to have the upthrow 



side not entirely removed by subsequent denudation " (see 



p. 12). 



The author then proceeds to describe in greater detail the various 

 formations, commencing with the lowest, the Skiddaw Slates. Prof. 

 Ilarkness and Dr. Nicholson have given much time to the working 

 out of tliis set of rocks, and, from tlieir fossils, refer them to the 

 Llandeilo series. They consist of slates and shales, with harder, 

 more gritty beds here and there. There are few fossils, but Grap- 

 tolites. Dr. Nicholson has, however, paid particular attention to 

 those organisms, and is the author of several valuable papers on the 

 subject. The Skiddaw Slates can be traced through the Isle of 

 Man, and seem to be represented, in part, in North Wales by the 

 Arenig group. 



He expresses a doubt as to whether the Green Slates and Por- 

 phyry are conformable on the Skiddaw Slates. Certainly the very 

 marked and sudden change in lithological character from soft slates 

 to hard felwpathic schists, grits, etc., would suggest a break of some 

 kind, and the occurrence of fragments like Skiddaw Slate in the 

 overlying breccias confirm this, as they show that the beds from 

 which they were derived were hardened, upheaved, and denuded 

 before the formation of the breccias ; but the identification of a piece 

 of slate must be very doubtful, and therefore we may say that we 

 have yet no data sufficient for the determination of this point. The 

 uniform character of the Skiddaw Slates over a very large area shows 

 that this is no mere local change, due to shifting currents, but must 

 be referred to some of those wide-spread changes which influenced the 

 great differences in successive geological formations and the life of 

 the period. Our author describes the Green Slates and Porphyry as 

 a vast series of bedded greenish-grej^ felspathic ashes or breccia 

 with interbeddod porphyries, and states that characteristic Bala 

 fossils occur in flaggy shales or hard grits near the top. It may be 

 open to question whether these fossiliferous bands should be bracketed 

 with the Green Slate series or with the overlying Bala Limestone 

 group. The district under the Penine range, in which they seem to 

 to occur lower down in the series, as described by Prof. Harkness, is 

 so tremendously faulted and masked by drift, that it is not safe to 

 infer that the section is complete between the points where only 

 these fossil bands have been found. For the solution of this ques- 

 tion also we must wait for further evidence. 



It has often been objected to some of our older terms, such as 

 greywacke, schist, etc., that they are too indefinite. Perhaps it is a 

 greater mistake to use terms too strictly defined in investigating im- 

 perfectly understood formations. Such terms as Porphyry and Ash- 



