September lo, 1908J 



NATURE 



463 



from the north entrance of the tunnel. It is observable 

 that the radio-activity of the granite increases as it 

 approaches the Usernmulde and attains its maximum 

 (14-1) where it dips beneatli the syncline. 



The means of radium-content in the several geological 

 sections into which the .'ourse of the tunnel is divisible 

 are as follows : — 



Granite of Finsteraaihorn 



Usernmulde 



St. Gotliard massif 



Tessinmulde 



77 

 4 9 

 3 9 

 3 4 



The central section, however, if considered without 

 reference to geological demarcations, would, as already 

 observed, come out as barely 33. And this is the value 

 of the radio-activity most nearly applicable to Stapff's 

 thermal subdivision of the region of low temperature. 



If we accept the higher readings obtained in the granite 

 as indicative of the radio-active state of this rock beneath 

 the Usernmulde, a satisfactory explanation of the differ- 

 ence of heat-flow from the central and northern parts of 

 the tunnel is obtained. Using the difference of gradient 

 as basis of calculation, as before, we find that a down- 

 ward extension of about six thousand metres would, if 



folding up of the great beds of sediment, and even their 

 over-thrusting for many miles. So that the mountaia 

 ranges of the world are not constituted from materials 

 rising from below, save in so far as these may form a 

 sustaining core, but of the slowly accumulating deposits 

 of the ages preceding the upheaval. 



The thickness of collected sediments involved in these 

 great events is enormous, and although uncertainty oftea 

 attends the estimation of the aggregate depths of sedi- 

 mentation, yet when we consider that unconformities 

 between the deposits of succeeding eras represent the 

 removal of vast masses of sediment to fresh areas of 

 deposition, and often in such a way as to lead to an 

 underestimate of the thickness of deposit, the observa- 

 tions of the geologist may well indicate the minor and 

 not the major limit. Witness the mighty layers of the 

 Huronian, Animikean, and Keweenawan ages where de- 

 posits measured in miles of thickness are succeeded by un- 

 recorded intervals of time, in which we know with certainty 

 that the tireless forces of denudation laboured to undo 

 their former work. Each era represents a slow and 

 measured pulse in the earth's crust, as if the overloading 

 and sinking of the surface materials induced the very 

 conditions required for their re-elevation. Such events, 



the outflow took place in an approximately vertical direc- 

 tion, account for the facts observed by Stapff. This depth 

 is in agreement with the result as to the downward 

 extension of the St. Gothard rocks as derived from the 

 comparison with the Simplon rocks. 



We are by no means in a position to found dogmatic 

 conclusions on such results ; they can only be regarded 

 as encouragement to pursue the matter further. The 

 coincidence must be remarkable which thus similarly 

 localises radium and temperature in roughly proportional 

 amounts, and permits us, without undue assumptions, to 

 explain such remarkable differences of gradient. There 

 is much work to be done in this direction, for well-known 

 cases exist where exceptional gradients in deep borings 

 have been encountered — exceptional both as regards excess 

 and deficiency. 



Radio-active Deposits and the Instability of the Crust. 



At the meeting of the British Association held last year 

 at Leicester, I read a note on the thermal effects which 

 might be expected to arise at the base of a sedimentary 

 accumulation of great thickness due to the contained 

 radium. 



The history of mount.iin building has repeated itself 

 many times : ages of sedhnentation, with attendant sink- 

 ing of the crust in the area of deposition, then upheaval, 



NO. 2028, VOL. 78] 



even in times when the crust was thinner and more 

 readily disturbed than it is now, must have taken vast 

 periods of time. The unconformity may represent as long 

 a period .as that of accumulation. In these Proterozoic 

 areas of America, as elsewhere on the globe and through- 

 out the whole of geological history, there has been a 

 succession in time of foldings of the crust always so 

 located as to uplift the areas of sedimentation, these up- 

 heavals being sundered by long intervals during which the 

 site of sedimentation was transferred and preparation 

 made for another era of disturbance. However long 

 deferred there seems to be only the one and inevitable 

 ending, inducing a rhythmic and monotonous repetition 

 surely indicative of some cause of instability attending the 

 events of deposition. 



The facts have been impressively stated by Dana : " A 

 mountain range of the common type, like that to which 

 the .'\ppalachians belong, is made out of the sedimentary 

 formations of a long preceding era ; beds that were laid 

 down conformably, and in succession, until they had 

 reached the needed thickness ; beds spreading over a 

 region tens of thousands of square miles in area. The 

 region over which sedimentary formations were in progress 

 in order to make, finally, the Appalachian range, reached 

 from New York to ."Mabama, and had a breadth of 100 

 to 200 miles, and the pile of horizontal beds along the 



