258 Mr. Hen wood on the Heaves 



It is stated that the great difficulty is to draw clear and consistent 

 lines of demarcation between these great primary divisions. They 

 pass into one another, and interchange some fossil species, especially 

 near their limits. Were it not for the magnificent sections of the old 

 red sandstone in the British Isles, and also in the north-eastern 

 parts of Europe (as now shown by Mr. Murchison and his fellow 

 labourers), the author asserts, that the second and third divisions 

 would probably be confounded and eventually pass under one common 

 name (including Upper Silurian and Devonian). In Belgium and the 

 Rhenish provinces the demarcation between them is quite arbitrary. 

 We there find Goniatites and long- winged Spirifers and other organic 

 types (first supposed to characterize the " Devonian system") abun- 

 dant in the Silurian rocks : and there is nothing in the physical 

 structure of those countries to suggest the separation of these two 

 divisions. By help of the British sections, combined with new facts 

 brought to light in Russia and America, the second division must 

 however maintain its place. 



Between the third and fourth divisions there appears to be a much 

 better marked separation, both physically and zoologically, than be- 

 tween the others. These two divisions (at least in North Wales) 

 differ in structure, interchange hardly any fossil species, and through 

 large districts are unconformable. Hence they belong to two systems, 

 and not to one, if the word system be used in a definite sense, and be 

 applied to the successive divisions (such as the Devonian). To avoid 

 incongruity of language, the author uses the word system in a ge- 

 neral sense ; and under the name Palaeozoic System describes the 

 whole series of formations comprehended under the four divisions 

 above described. In this great descending series the " Silurian 

 system" (in the sense in which the words were first used) stands 

 in the place of the third, and the upper part of the fourth primary 

 division. 



XXXIX. On the Heaves of Metalliferous Veins by Cross-veins. 

 —Part II. By William Jory Henwood, KB.S., F.G.S., 



Mining Engineer, eye* 



(II.) TNTERSECTIONS of lodes affording different ores 

 ■*- by cross-veins of different compositions. — Throughout 

 tracts of small extent the composition of the rocks is usually, 

 in some measure, uniform, so that the lodes within such given 

 tracts present nearly the same characters. This general fact 

 applies with even greater certainty to the cross- veins, whose 

 characters are still more uniform ; for they consist for the most 

 part of quartz and clayey portions of the contiguous rocks ; 

 and with the exception of lead ores, and these not abundant, 

 the metallic matters which they contain are in small quanti- 

 ties, and dispersed through very limited portions of them. 



* Communicated by the Author .- Part I. will be found in our preceding 

 Number, p. 180. 



