GEOLOGY. 295 



The former mode of progression is that recognized by the sliding theory ; 

 the second is that recognized by what has been termed the viscous theory 

 of Professor Forbes. The viscous theory appeared to be generally recog- 

 nized. Still, to many persons, it seemed difficult to reconcile the property of 

 viscosity with the fragility and apparent inflexibility and inextensibility of 

 ice itself. On the other hand, if this property of viscosity, or something of 

 the kind, were denied, how could we account for the fact of different frag- 

 ments, into which a glacier is frequently broken, becoming again united into 

 one continuous mass ? Dr. Tyndall has, I conceive, solved the difficulty. 

 Glacial ice, unlike a viscous mass, will bear very little extension. It breaks 

 and cracks suddenly; but the separate pieces, when subsequently squeezed 

 together again, become, by regelation (as it is termed), one continuous mass. 

 After some general remarks on the cause of the laminated structure of gla- 

 ciers, during which he remarked that there was no doubt Dr. Tyndall was 

 right in supposing the laminae of blue and white ice to be perpendicular to 

 the directions of maximum pressure, he said that it remained to be decided 

 whether the explanations which had been offered were correct; but the 

 actual perpendicularity of the lamina? of ice to the directions of maximum 

 pressure within a glacier, and the probable perpendicularity to those direc- 

 tions of the laminae in rock masses of laminated structure, would seem to es- 

 tablish some relation between these structures in rocks and glacial ice, giving 

 an interest to this peculiar structure in the latter case, which it might not oth- 

 erwise appear to possess for one who should regard it merely as a geologist. 



ON THE GENERAL AND GRADUAL DESICCATION OF THE EARTH 



AND ATMOSPHERE. 



At the Leeds meeting of the British Association, a paper, entitled as 

 above, was read by Mr. J. S. Wilson, in which the author drew attention to 

 the fact, that those who had travelled in continental lands, especially in and 

 near the tropics, had been forced to reflect on the changes of climate that 

 appeared to have occurred. There were parched and barren lands, dry river 

 channels and waterless lakes, and, not unfrequently, traces of ancient hu- 

 man habitations, where large populations had been supported, but where 

 all was now desolate, dry, and barren. After quoting largely from the works 

 of various travellers and writers (among the latest of whom was Dr. Liv- 

 ingston), and giving interesting descriptions of dried-up rivers and desolate 

 tracts of country in Australia, Africa, Mexico, and Peru, which had formerly 

 been inhabited by man, Mr. Wilson concluded that there was a gradual 

 solidifying of the aqueous vapors, and, consequently, of water, on the face of 

 this terrestrial world, which, he inferred, was approaching a state in which 

 it will be impossible for man to continue an inhabitant. 



ON THE FORMATION OF CONTINUOUS TABULAR MASSES OF STONY 



LAVA ON STEEP SLOPES. 



The question whether lava can consolidate on a steep slope, so as to form 

 strata of stony and compact rock, inclined at angles of from 10 to more 

 than 30, has of late years acquired considerable importance, because geolo- 

 gists of high authority have affirmed that lavas which congeal on a declivity 

 exceeding 5 or 6 are never continuous and solid, but are entirely composed 

 of scoriaceous and fragmentary materials. From the law thus supposed to 

 govern the consolidation of melted matter of volcanic origin, it has been 



