412 T. M. Reade — Cause of Active Compressive Stress 



consequent on a rise of temperature since the Glacial Period.** 

 If the Glacial Period had been sufficiently prolonged to have 

 affected the isogeotherms down to a considerable depth where 

 the rocks are in tightly compressed contact, it is conceivable 

 that the rise of temperature in the Post-glacial Period — again 

 assuming a sufficient length of time has elapsed — may have 

 been enough in some instances to create a low domical uplift, 

 but it does not seem to me to be likely that the pressure from 

 this cause could accumulate in surface rocks subject to atmo- 

 spheric changes over such extended periods. 



Before committing myself even to any suggested explanation 

 of these extremely interesting phenomena I was desirous of 

 ascertaining whether the districts described were affected by 

 faulting, and if so to what extent and in which direction. 

 Professor J. W. Spencer, who was staying with me at the time, 

 kindly offered to make enquiries, but I am sorry to say the 

 result has not been very encouraging, indeed very barren. As 

 regards Ohio the State Geologist, Mr. Edward Orton, says that 

 faults are exceedingly rare in Ohio geology but joints are finely 

 shown at Berea; the master joints being a few degrees north 

 of east and the main joints of all the Ohio rocks as far as he 

 can recall the facts, except in one instance, have the same 

 direction. 



It appears to me that the cause of these active evidences of 

 lateral pressure must be sought in the differential movements 

 to which it is well known the crust of the earth is subjected. 

 Since the Glacial period, in the British Isles, there are the 

 strongest evidences of vertical movements both of subsidence 

 and elevation having taken place. Having paid great atten- 

 tion both to Post glacial and Glacial geology during the past 

 twenty years I consider the evidences are overwhelming. 

 Since the marine bowlder clay of the plains was laid down 

 there have been two movements of elevation and two of de- 

 pression to the extent of several hundred feetf but as the evi- 

 dences of maximum movement are submerged we cannot 

 estimate it. The well known sand and gravel glacial drift with 

 shells on Moel Try fan, North Wales, at an elevation of nearly 

 1400 feet above the sea has long been taken by most English 

 Geologists as convincing evidence of a vertical movement of 

 elevation to that extent since the beds were laid down and 

 notwithstanding the views of some extreme glacialists I must 

 be pardoned if I still- consider them a monument of geologi- 

 cally recent elevation. It is true some of the American geolo- 



* "Some Geologic Wrinkles," Proc. of American Assoc, for the Advancement 

 of Science, Thirty-fifth MeetiDg, 1886. 



f Geology and Physics of the Post Glacial Period, etc. Proc. Liverpool. GeoL 

 Soc, Session 1871-2. 



