156 
until the whole cavity is filled at the expense of the sur- 
face. Now I know that the instances of subsidence are 
very curious, but their being objects of curiosity implies 
some degree of rarity. I believe the complete filling up 
of old mines from this sinking process to be slow, irregular, 
and by no means to be depended on. This is implied also 
in several passages of these reports. 
We have the river Sirhowey flowing over the works of 
Risca colliery. Indeed, among the many mines of all kinds 
carried under rivers or the sea, I remember but two or 
three instances of flooding by irruption of water from the 
surface. 
I have omitted many interesting particulars, out of regard 
to your time, and to the authors of other papers. The 
printed documents will well repay the attention of persons 
of all ranks engaged in such undertakings. It would be a 
great mistake to suppose that the appointment of inspectors 
in the least degree relieves proprietors or managers of 
collieries from responsibility, or that it will at all cramp 
their own exertions for the preservation of their property, 
and of the lives of their workmen. The intention is, and 
if all classes concerned do their duty, the effect will be, 
to assist, as well as to stimulate, individual exertion. It 
is much to be hoped that from the time when the inspectors 
about to be appointed commence their operations, they will 
collect, record, and publish all such particulars of every 
explosion of mark as may furnish to themselves, other in- 
spectors, proprietors, and agents of every description and 
name, the means of learning from them what to adopt 
and what to avoid, for the purpose of preventing, or ren- 
dering less destructive, these calamities. 
I do not deem it needful to dwell long upon that unde- 
niable and prominent source of danger — the carelessness 
or fool-hardiness of workmen. We find from the evidence 
