This is undoubtedly in most cases a true and sufficient answer, yet we think the fragmentariness of the geological record has been overstated. While it is true that there are many and wide gaps in the record; while it is true, also, that even where the record is continuous many forms may not have been preserved, yet there are some cases, especially in the Tertiary fresh-water deposits, where the record is not only continuous for hundreds of feet in thickness, but the abundance of life was very great, and the conditions necessary for preservation exceptionally good. In such cases the number of fossil species found on each horizon seems to be as great as in existing faunas over equal space. The record in these cases seems to be continuous and without break, and crowded with fossil forms; and yet, although the species change greatly, and perhaps many times, in passing from the lowest to the highest strata, we do not usually, it must be acknowledged, find the gradual transitions we would naturally expect, if the change were effected by gradual transformations. The incompleteness of the record, therefore, although a true and important cause, is not the whole cause. In further and completer answer to this greatest of all objections, we will throw out the following suggestions: 2. We must remember that considerable latitude is allowed by the anti-derivationists to _variation of species;_ so much so, indeed, that it is often difficult to draw the line between well-marked varieties and closely-allied species. Now, according to the derivationist, these strong varieties, breeding usually true, are naught else than commencing species. 3. On every side and everywhere, both in existing faunas and in fossil forms, but especially in the latter, we find innumerable examples of transitions, or intermediate forms, between all the _higher groups_, such as genera, families, orders, and classes. It is, in fact, by means of these that the great law of differentiation from generalized types has been established. It is, therefore, only between _species_ that such intermediate forms are rare. 4. But even between species such intermediate forms, though rare, have been pointed out, both in existing and in extinct faunas. But the opposition contend that, in all such cases, the previously supposed species are only varieties. We have already (page 61) spoken of the obvious fallacy involved in this position. Species are first defined as forms distinct and without intermediate links, and then we are challenged to find such links; and when, with much labor, we find them, they say the supposed species are not species, but only varieties. But there are some cases in which this subterfuge will not do. There are cases in which the transitions are between forms so extreme that they can not, by any stretch of the term, be called varieties. We will select and dwell upon but one striking example, viz., the fossil forms of the Tertiary fresh-water deposits of Steinheim.