the summer of 1918 and the measurements and tabulation finished soon after. I wish gratefully to acknowledge the courtesy of the editors of the Astrophysical Journal and the Bulletin of the American Geographical Society for permission to use illustrations and extracts from articles of mine which they have published. Plate 9 and figure 31 in the text are from the former journal. Thanks are also extended to Professor Ellsworth Huntington for the use of several text-figures which first appeared in my chapter of his work (1914).
TREES SUITABLE FOR CLIMATIC STUDY.
During the course of this investigation the wood and growth of numerous species of trees have been examined with reference to their adaptability to the purposes herein described. The collections visited include several in London, especially one in the South Kensington Museum, fossils in the Jermyn Street Museum, the lumber-yards of Messrs. W. W. Howard Bros. & Company, tree sections and fossils in the geological museum at Berlin, fossils in the lignite beds of Grube Ilsa near Dresden, and fossils chiefly in Munich and Vienna. In
Table 1.—List of trees in the Jessup collection whose rings were counted.
| Scientific name. | Common name. | Locality. | Approximate center, A. D. | Possible periods. | Quality of ring sequence. |
| Pinus torreyana | Torrey pine | San Diego, Cal | 1790 | 11 years | |
| Pinus radiata | Monterey pine | Monterey, Cal | 1855 | 22 years | |
| Pinus monticola | Western white pine | Oregon | 1641 | 11 years; Brückner | |
| Pinus strobiformis | Mexican white pine | Southern Arizona | 1706 | 22 years | |
| Pinus strobus | White pine | Nova Scotia | 1740? | 22 years; Brückner | Fair |
| Pinus tæda | Loblolly pine | Florida | 1731 | ||
| Pinus echinata | Short-leaved pine | Missouri | 1650 | ||
| Tsuga heterophylla | Western hemlock | Canada northwest coast | 1700 | Uncertain | |
| Tsuga caroliniana | Carolina hemlock | Carolina | 1697 | Poor. 22yr.; Brückner | Good |
| Tsuga canadensis | Canadian hemlock | Nova Scotia | 1525 | 11 years; Brückner | Good |
| Pseudotsuga macrocarpa | Bigcone fir | Southern California | 1480? | 11 years | Good |
| Pseudotsuga mucronata | Douglas fir | Oregon | 1315 | 11 years | Good |
| Picea sitchensis | Tideland spruce | Northwest coast | 1798 | Very good | |
| Picea rubens | Red spruce | Nova Scotia | 1610 | ||
| Sequoia gigantea | Bigtree | California | 550 | Brückner | Good |
| Taxodium distichum | Bald cypress | Florida | 1670? | ||
| Cupressus macnabiana | Macnab cypress | Northern California | 1760 | Very good | |
| Toxylon pomiferum | Osage orange | Southern Arkansas | 1765 | Fair | |
| Ulmus fulva | Slippery elm | Missouri | 1770 | 20 years |
