Page:The Journal of geology (IA journalofgeology11893univ).pdf/435

Mr. White has described, under the name of Tæniopteris missouriensis, a new and well characterized fern from the Lower Coal-measures in the vicinity of Clinton, Henry County, Missouri. Botanically, it is of particular interest in that it combines the so-called tæniopteroid and alethopteroid types of structure, while geologically it is of much value in supplying a readily identified stratigraphic mark in a part of the Carboniferous not especially rich in fossil plants. After thoroughly describing it and considering its specific and generic resemblances, the author discusses at length its suggested genetic relations and represents in a graphic manner a scheme of its probable ancestors and line of descent.

The paper confines itself to the characteristic distribution of precipitation throughout the year and gives the rainfall types of the country.

(a) The best defined type of rainfall within the United States is that which dominates the Pacific coast region as far east as western Utah. The characteristic features are a very heavy precipitation during midwinter, and an almost total absence of rain during the late summer. (b) The characteristics of the Mexican type, dominating Mexico, New Mexico and western Texas, are a very heavy precipitation after the summer solstice and a very dry period after the vernal equinox. August is the month of greatest rainfall, while February, March and April are almost free from precipitation. (c) The Missouri type covers the greatest area, dominating the watersheds of the Arkansas, Missouri and upper Mississippi rivers, and of lakes Ontario and Michigan. It is marked by a very light winter precipitation, followed in late spring and early summer by the major portion of the yearly rain, the period when it is most beneficial to the growing grain.