This is very vague, but the phenomena are so remarkable, and so very imperfectly known at present, that nothing but suggestion can be attempted.
_Concluding Remarks on the 'Canals.'_ In this somewhat detailed exposition of a possible, and, I hope, a probable explanation of the surface-features of Mars, I have endeavoured to be guided by known facts or accepted theories both astronomical and geological.

I think I may claim to have shown that there are some analogous features of terrestrial rock-structure to serve as guides towards a natural and intelligible explanation of the strange geometric markings discovered during the last thirty years, and which have raised this planet from comparative obscurity into a position of the very first rank both in astronomical and popular interest.
This wide-spread interest is very largely due to Mr.Lowell's devotion to its study, both in seeking out so admirable a position as regards altitude and climate, and in establishing there a first-class observatory; and also in bringing his discoveries before the public in connection with a theory so startling as to compel attention.

I venture to think that his merit as one of our first astronomical observers will in no way be diminished by the rejection of his theory, and the substitution of one more in accordance with the actually observed facts.
APPENDIX.
_A Suggested Experiment to Illustrate the 'Canals' of Mars._ If my explanation of the 'canals' should be substantially correct--that is, if they were produced by the contraction of a heated outward crust upon a cold, and therefore non-contracting interior, the result of such a condition might be shown experimentally.
Several baked clay balls might be formed to serve as cores, say of 8 to 10 inches in diameter.

These being fixed within moulds of say half an inch to an inch greater diameter, the outer layer would be formed by pouring in some suitable heated liquid material, and releasing it from the mould as soon as consolidation occurs, so that it may cool rapidly from the _outside._ Some kinds of impure glass, or the brittle metals bismuth or antimony or alloys of these might be used, in order to see what form the resulting fractures would take.

It would be well to have several duplicates of each ball, and, as soon as tension through contraction manifests itself, to try the effect of firing very small charges of small shot to ascertain whether such impacts would start radiating fractures.