Elizabeth Cary Agassiz, Louis Agassiz: his life and correspondence, third edition

[706] ages, similar types inhabited shallow seas? Of the fact there can be no doubt, for it is not difficult to adduce satisfactory evidence of the shoal-like character of the Silurian deposits of the State of New York; their horizontal position, combined with the gradual recession of the higher beds in a southerly direction, leaves no doubt upon this point; and in the case of the jurassic formation alluded to above, the combination of the crinoids with fossils common upon coral reefs, and their presence in atolls of that period, are satisfactory proofs of my assertion. What does it mean, then, when we find the Pentacrinus and Rhizocrinus of the West Indies in deep water only? It seems to me that there is but one explanation of the fact, namely, that in the progress of the earth's growth, we must look for such a displacement of the conditions favorable to the maintenance of certain lower types, as may recall most fully the adaptations of former ages. It was in this sense I alluded, in my first letter to you, to the probability of our finding in deeper water representatives of earlier geological types; and if my explanation is correct, my anticipation is also fully sustained. But do the deeper waters of the present constitution of our globe really approximate