Young Stensen seems to have been the object [{152}] of solicitude on the part of a number of the good, elderly women with whom he was brought in contact. He discussed with Signora Arnolfini the great difficulty he had in believing the mystery of the Eucharist. Another good woman, the Signora Lavinia Felice, seeing how interested he was in things Catholic, succeeded in bringing him to the notice of a prominent Jesuit in Florence. As his friend, Sister Maria Flavia, had recommended the same Father to him, he followed the advice all the more readily, and it was not long before his last doubts were solved.
It was after his conversion that Stensen received his invitation to become the professor of anatomy at the University of Copenhagen. Much as he had become attached to Florence, the thought of returning to his native city was sweet; and then besides he hoped that he might be able to influence his countrymen in their views toward the Catholic Church. It was not long, however, before the bigotry of his compatriots made life so unpleasant for him in Copenhagen that he resigned his position and returned to Italy. Various official posts in Florence were open for him, but now he had resolved to devote himself to the service of the Church, and so he became a priest. His contemporary, the Cardinal Archbishop of Florence, said with regard to him: "Already as a member of a Protestant sect he had lived a life of innocence and had practised all the moral virtues. After his conversion he had marked out for himself so severe a method of life and had [{153}] remained so true to it that in a very short time he reached a high degree of perfection." The Archbishop does not hesitate to say that he had become a man of constant union with God and entirely dead to himself. There was very little hesitation, then, in accepting him as a candidate for the priesthood, and as his knowledge of theology was very thorough, most of the delay in raising him to that dignity came from his own humility and his desire to prepare himself properly for the privilege. He made the exercises of St. Ignatius as part of his preparation, and after his ordination it was a source of remark with how much devotion he said his first and all succeeding Masses. It was not long before the piety of Stensen's life attracted great attention. At this time he was in frequent communication with such men as Spinoza and Leibnitz, the distinguished philosophers. It is curious to think of the ardent mystic, the pantheistic philosopher, and the speculative scientist, so different in character, having many interests in common.
It was during these years in Italy that Stensen did what must be considered, undoubtedly, his most important work, even more important, if possible, than his anatomical discoveries. This was his foundation of the science of geology. As has been well said in a prominent text-book of geology, his book on this subject sets him in that group of men who as prophets of science often run far ahead of their times to point out the path which later centuries will follow in the road of [{154}] knowledge. It is rather surprising to find that the seventeenth century must enjoy the privilege of being considered the cradle of geological knowledge. There is no doubt, however, that the great principles of the science were laid down in Stensen's little book, which he intended only to be an introduction to a more extensive work, but the latter was unfortunately never completed, nor, indeed, so far as we are able to decide now, ever seriously begun.
One of the basic principles of the science of geology Stensen taught as follows: "If a given body of definite form, produced according to the laws of nature, be carefully examined, it will show in itself the place and manner of its origin." This principle he showed would apply so comprehensively that the existence of many things, hitherto apparently inexplicable, became rather easy of solution. It must not be forgotten that before this time two explanations for the existence of peculiar bodies, or of ordinary bodies, in peculiar places, had been offered. According to one school of thought, the fossils found deep in the earth, or sometimes in the midst of rocks, had been created there. It was as if the creative force had run beyond the ordinary bounds of nature and had produced certain things, ordinarily associated with life, even in the midst of dead matter. The other explanation suggested was that the flood had in its work of destruction upon earth caused many anomalous displacements of living things, and had buried some of the [{155}] animals under such circumstances that later they were found even beneath rocks, or deep down in the earth, far beyond where the animals could be supposed to have penetrated by any ordinary means during life.
Stensen had observed very faithfully the various strata that are to be found wherever special appearances of the earth's surface were exposed, or wherever deep excavations were made. His explanation of how these various strata are formed will serve to show, perhaps better than anything else, how far advanced he was in his realization of ideas that are supposed to belong only to modern geology. He said: "The powdery layers of the earth's surface must necessarily at some time have been held in suspension in water, from which they were precipitated by their own weight. The movement of the fluid scattered the precipitate here and there and gave to it a level surface."
"Bodies of considerable circumference," Stensen continues, "which are found in the various layers of the earth, followed the laws of gravity as regards their position and their relations to one another. The powdery material of the earth's strata took on so completely the form of the bodies which it surrounded that even the smallest apertures became filled up and the powdery layer fitted accurately to the surface of the object and even took something of its polish."
With regard to the composition of the various strata of the earth, the father of geology [{156}] considered that if in a layer of rock all the portions are of the same kind there is no reason to deny that such a layer came into existence at the time of creation, when the whole surface of the earth was covered with fluid. If, however, in any one stratum portions of another stratum are found, or if the remains of plants or animals occur, there is no doubt that such a stratum had not its origin at the time of creation, but came into existence later.
If there is to be found in a stratum traces of sea salt, or the remains of sea animals, or portions of vessels, or such like objects, which are only to be encountered at the bottom of the sea, then it must be considered that this portion of the earth's surface once was below the sea level, though it may happen that this occurred only by the accident of a flood of some kind. The great distance from the sea, or other body of water, at the present time, may be due to the sinking of the water level in the neighborhood, or by the rising up of a mountain from some internal terrestrial cause in the interval of time. He continues:--
If one finds in any layer remains of branches of trees, or herbs, then it is only right to conclude that these objects were brought together because of flood or of some such condition in the place where they are now found. If in a layer coal and ashes and burnt clay or other scorched bodies are found, then it seems sure that some place in the neighborhood of a watercourse a fire took place, and this is all the more sure when the whole layer consists of ashes and [{157}] coal. Whenever in the same place the material of which all the layers is composed is the same, there seems to be no doubt that the fluid to which the stratum owes its origin did not at different times obtain different material for its building purposes.
In respect to the mountains and their formation, Stensen said very definitely:--