1014 REPORT—1885. 
The probable origin of these disturbances has naturally been much canvassed , 
and blasting in quarries, shot-firing in collieries, and the passing of railway trains. 
have in turn been accused of causing them, and, on examination, have been found 
‘not guilty.’ At the present time there is no doubt whatever that the shocks are 
due to some natural cause. As to what that natural cause may be there is, per- 
haps, room for difference of opinion. 
My friend Mr. M. Walton Brown, of the Coal Trade Offices at Newcastle-upon- 
Tyne, in a paper read in 1884 before the North. of England Institute of Mining and 
Mechanical Engineers, refers to the Sunderland shocks as being genuine earth- 
tremors, but I think that their extremely local character—setting aside many other 
points inconsistent with this view of their origin—is conclusive against this being 
sO. 
In another paper, read, at the same time as Mr. Walton Brown’s, before the same 
Tnstitute, I brought forward a number of facts tending to connect the phenomena 
above referred to with certain peculiarities in the geological structure of the dis- 
trict. Since that time, the shocks having continued more or less continuously, 
and evidence of all kinds with regard to them having accumulated, I wish to lay 
my more mature views on the subject before Section C, in the hope that members: 
in discussing them may help to elicit the truth. 
Sunderland stands upon the Permian Magnesian Limestone, of which there 
is from 300 to 400 feet beneath the town. This rock is riddled with cavities 
of every size and shape. The smaller ones give a vesicular aspect to the stone in 
many places, but the larger ones are often true caverns, due to the combined action 
of mechanical and chemical agencies. Many of them may be accounted for by 
noting how frequently masses, both large and small, and of all shapes of soft pul- 
verulent matter occur in the midst of the most compact and hard portions of the 
limestone. How easily such soft, incoherent, earthy rock, or ‘ marl,’ as it is called 
locally, can be removed by the merest percolation of rain-water where there is an 
outlet needs no proof, and that caverns would result and have resulted from such 
removal is clear. This action is indeed chiefly mechanical, but there is also going 
on at the same time a yery considerable destruction or removal of rock by the 
ordinary chemical action of rain-water on limestone. 1 have shown elsewhere 
that-every thousand gallons of Sunderland water, pumped up and ultimately thrown 
into the sea, represents one pound of stone abstracted. In each year the Water 
Company robs the Magnesian Limestone in this manner of about forty cubic yards 
of rock, and, of course, much more is carried off annually by natural channels. 
How large some of the cavities are which form water-cisterns in this rock may 
be gathered from the fact that when, in sinking a shaft at Whitburn Colliery im 
1874, one of them was unfortunately tapped, it yielded 11,612 gallons of water 
per minute for a month. 
_* The rock then immediately underlying Sunderland is a mass of calcareous stone 
mostly hard and compact, but cellular in places and earthy and friable in others, 
often cavernous on a large scale, full of water, and through its action continually 
parting with its substance, and thus enlarging the cavities within tt. ‘ 
Under conditions such as these, it follows necessarily that the vaults of cavities: 
must, from time to time, give way, and, in collapsing, produce concussions accom- 
panied by noise, but limited in the area over which their effects would be felt. In 
short: it seems to me that we have in such natural stone-falls at moderate depths a. 
sufficient explanation of the Sunderland earth-shocks. 
In the paper before alluded to I pointed out that this theory explains equally 
well all the facts connected with the singular fissures full of breccia (‘ breccia- 
gashes’), which are common in the Magnesian Limestone of Durham, and have 
been a standing puzzle hitherto to Lyell, Sedgwick, and all the geologists who 
have published accounts of the magnificent sections exhibited along the coast 
between South Shields and Sunderland. 
Quite recently very similar shocks have been felt, as I am informed, in the 
neighbourhood of Middlesborough, where it is probable that they are due to the 
withdrawal of rock-salt, which has been going on there of late years only. In this 
case the depth at which the cavities are being formed and rock-collapses are, as I 
