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 scale, and the investigation of deposits now in the course of formation, teach us that, from the first dawn of animated nature up to the present hour, this prolific family has never ceased its activity. England may boast that the sun never sets upon her empire; but here is an ocean-realm whose subjects are literally more numerous than the sands of the sea. We cannot count them by millions simply, but by hundreds of thousands of millions. Indeed, it is futile to speak of numbers in relation to things so uncountable. Extensive rocky strata, chains of hills, beds of marl, almost every description of soil, whether superficial or raised from a great depth, contain the remains of these little plants, in greater or less abundance. Some tracts of country are literally built up of their skeletons. No country is destitute of such monuments; and in some they constitute the leading features in the structure of the soil. The world is a vast catacomb of Diatomaceæ; nor is the growth of those old dwellers on the earth diminished in its latter days!"

Whether living or dead, diatoms are very beautiful objects under the microscope; but it is impossible to give in words a distinct idea of their complex forms and delicate markings. In the muddy waters of the Thames we meet with some lovely varieties. Amongst them we may find one or two which may be roughly compared with some