78 Notices of Memoirs — Dr. T. S. Hunt on the Appalachians. 



sbire, and the Shetland Isles ; these Dr. Hunt is convinced will be 

 found to belong to a period anterior to the deposition of the Cambrian 

 sediments, and will correspond with the newer gneissic series of the 

 Appalachians. 



Kocks regarded by Harkness as identical with these of the 

 Scottish Highlands also occur in Donegal and Mayo. 



From an examination of a large collection of the crystalline rocks 

 of this ai-ea Dr. Hunt is enabled to assert the existence in the north- 

 west of Ireland, of the second and third series of crystalline schists. 

 He also observes that micaceous schists, with andalusite (chiasto- 

 lite) of the type of the White Mountain series, occur on Skiddaw, 

 in Cumberland. 



He states his conviction that in the study of the ci'ystalline schists, 

 the persistence of certain mineral characters must be relied upon as 

 a guide, and that the language used by Delesse in 1847 will be 

 found susceptible of a wide application to crystalline strata — "Eocks 

 of the same age have most generally the same chemical and minera- 

 logical composition, and that reciprocally, rocks having the same 

 chemical composition and the same minerals, associated in the same 

 manner, are of the same age." 



Turning now to the genesis of the crystalline schists whose geo- 

 logical relations he has just discussed, Dr. Hunt observes that the 

 gneisses, mica-schists, and argillites of various geological periods do 

 not differ very greatly in chemical constitution from modern me- 

 chanical sediments, and are now very generally regarded as resulting 

 from a molecular re-arrangement of similar sediments formed in 

 earlier times by the disintegration of pi'eviously existing rocks not 

 very unlike them in composition. 



The whole history of these rocks shows that their various alter- 

 nating strata were deposited under conditions of sedimentation very 

 like those of more recent times. In the Laurentian system, great 

 limestone formations are interstratified with gneisses, quartzites, and 

 even with conglomerates. All analogy, moreover, leads us to con- 

 clude that even at this early period life existed at the surface of the 

 planet, and such has indeed proved to be the case by the discovery 

 of the Eozoon Canadense. Great accumulations of iron-oxyd, beds of 

 metallic sulphides and of graphite, exist in these ancient strata, and 

 we know of no other agency, says Dr. Hunt, than that of organic 

 matter, capable of generating these products. 



las^viE^w^s. 



I. — The Student's Manual of Geologt, By J. Beete Jukes, 

 M.A., F.E.S. Third Edition, re-cast, and in great part re-written. 

 Edited by Archibald Geikie, F.E.S. 8vo. pp. 778. (Edin- 

 burgh : A. & C. Black, 1872.) 



THE value of any Manual in relation to the branch of Natural 

 Science of which it treats — and especially a Manual of Geology 

 — depends to a very large extent upon the antecedents of its author, 



