Cleavage measurements
19,298 cleavage measurements from published US geologic maps, recorded as strike and dip and cited to the map each came from — 2% of the Atlas.
What it is
Cleavage is a fine, penetrative parting produced by layer-parallel shortening at low metamorphic grade — slaty cleavage being the familiar case, where a mudstone becomes a slate that splits on a plane unrelated to its bedding.
What makes cleavage disproportionately useful is that it typically forms axial-planar to the folds it accompanies: the cleavage plane approximately contains the fold's axial surface. A cleavage reading taken on one limb therefore constrains the geometry of a fold whose hinge may not be exposed anywhere nearby, and the intersection of cleavage with bedding is a lineation parallel to the local fold axis.
The boundary between cleavage and foliation is a matter of grade and of the mapping geologist's judgement, and sources here draw it differently. The raw published term travels with every row.
How the Atlas records it
Every cleavage row carries an azimuth and an inclination in one convention
(right-hand-rule strike and dip), a position in WGS 84 with the publisher's
own location confidence, the raw type term as the source published it, and the citation of the source map.
Selections export as CSV with a companion sources.csv of citations.
Which sources have it
| Source | Measurements | Share |
|---|---|---|
| NPS GRI parks | 7,001 | 36% |
| USGS NGMDB GeMS | 3,226 | 17% |
| Vermont Geol. Survey | 2,763 | 14% |
| NGMDB legacy quads | 1,820 | 9% |
| USGS SIM quads (NE) | 1,364 | 7% |
| Washington Geol. Survey | 839 | 4% |
| USGS data releases · MRDS | 643 | 3% |
| Virginia DGMR | 577 | 3% |
| Oregon DOGAMI (OGDC-8) | 447 | 2% |
| Wisconsin WGNHS | 266 | 1% |
| Alaska DGGS | 264 | 1% |
| Pennsylvania Geol. Survey | 50 | <1% |
| South Dakota SDGS | 38 | <1% |
Where it is
| State | Measurements | Share |
|---|---|---|
| Vermont | 3,657 | 19% |
| California | 1,954 | 10% |
| Pennsylvania | 1,877 | 10% |
| New Jersey | 1,807 | 9% |
| Virginia | 1,514 | 8% |
| Maryland | 1,367 | 7% |
| North Carolina | 1,129 | 6% |
| Maine | 1,054 | 5% |
| Washington | 855 | 4% |
| New Hampshire | 735 | 4% |
| Colorado | 657 | 3% |
| Oregon | 490 | 3% |
| Alaska | 455 | 2% |
| Tennessee | 390 | 2% |
| Montana | 351 | 2% |
| Wisconsin | 265 | 1% |
| Idaho | 214 | 1% |
| South Dakota | 140 | <1% |
| South Carolina | 134 | <1% |
| Connecticut | 45 | <1% |
| West Virginia | 44 | <1% |
| New Mexico | 36 | <1% |
| Arizona | 33 | <1% |
| New York | 30 | <1% |
| Michigan | 13 | <1% |