In Ireland, there are the same fossils, the same shells and the same sea bodies, as appear in America, and some of them are found in no other part of Europe.

Writing well is at one and the same time good thinking, good feeling, and good expression; it is having wit, soul, and taste, all together.

There are several kinds of truths, and it is customary to place in the first order mathematical truths, which are, however, only truths of definition. These definitions rest upon simple, but abstract, suppositions, and all truths in this category are only constructed, but abstract, consequences of these definitions ... Physical truths, to the contrary, are in no way arbitrary, and do not depend on us.

One can descend by imperceptible degree from the most perfect creature to the most shapeless matter, from the best-organised animal to the roughest mineral.

An Individual, whatever species it might be, is nothing in the Universe. A hundred, a thousand individuals are still nothing. The species are the only creatures of Nature, perpetual creatures, as old and as permanent as it. In order to judge it better, we no longer consider the species as a collection or as a series of similar individuals, but as a whole independent of number, independent of time, a whole always living, always the same, a whole which has been counted as one in the works of creation, and which, as a consequence, makes only a unity in Nature.

We can only penetrate the rind of the earth.

There is nothing good in love but the physical part.