Thomas K. Macbride.
This small sum enabled me to go with my son George into the chalk of Kansas, where we discovered the splendid specimen of a mosasaur, now in the museum of Iowa University. But for the timely assistance given me when I most needed help, it is doubtful whether Iowa would have secured this treasure. My months of patient labor on the leaves had convinced the authorities that my work on the mosasaur would be faithfully done.
Before closing this account of my work in the Dakota Group, I should like to say a few words about the manner in which the nodules are formed around leaf impressions, a subject of which I have made a careful study during years of exploration. The illustrations (Fig. [5], a and b) show the nodules before they are opened, and the open specimens before they have been trimmed, as in the other cuts.
The mother rock, or matrix, as it is called, from which these concretions come, is quite soft and easily disintegrates into yellowish sand under the influences of the weather. Through this yellowish sandstone are scattered countless leaf impressions and their counterparts, but on account of the softness of the matrix it is impossible to work out any leaves from the inside of the rock masses, and we should lose them altogether were it not for the following natural process:
Falling from the trees that grew along the shore of the Cretaceous Ocean, these leaves were covered with sand by the incoming tide. Some, falling stem first, were turned over into a U-shape; others are found lying flat, and others again at various angles. The sand, accumulating through the years, finally became consolidated, and, being in course of time exposed to the air, began to “weather.” In the meantime the iron coloring matter of the vegetation had been dissolved out by the water and distributed through the rock mass. As the rock weathers away, the leaf impressions are hardened by the iron that has been dissolved out of the sandy mass by water holding acids in solution.
As the soft rock about them continues to wear away, the nodules begin to appear above the surface, at first only as bumps slightly elevated above the surrounding rock, but in time as complete concretions, with the form of the leaves imprisoned within, which are left standing on pedestals no thicker than a lead pencil.
Then the first storm of rain or hail breaks them from their moorings; they become independent, are reduced in size, and constantly hardened, so that often a nodule is almost pure iron ore a fraction of an inch in thickness.
So the process goes on and will continue until all the leaves within the parent rock have been protected by an iron envelope; and it is this natural process alone which can save these beautiful impressions from falling to pieces when the sand is freed from the rock by disintegration.
The locality from which I collected these specimens I have named the Betulites locality, on account of the abundance of birch leaves of many varieties which have been found there. It was discovered by the late Judge E. P. West, collector for the University of Kansas, and Professor Lesquereux honored him by calling one species Betulites westii. He made a wonderful collection of Dakota leaves for the University, many of them new to science. The locality is about a mile in length and tops the highest hills in Ellsworth County.
I have no record of the thousands of fossil leaves I have collected from the sandstone of central Kansas. I have never kept a single specimen for myself, although I love them dearly, and it has often been hard to give them up. But the object of my life has been to advance human knowledge, and that could not be accomplished if I kept my best specimens to gratify myself. They had to go, and they went, often for less than they cost me in labor and expense, into the hands of those who could give authoritative knowledge of them to the world, and preserve them in great museums for the benefit of all.