CRUMBLE 



Wind blowing in a direction approximately 

 90 degrees from the course. One blowing in a 

 direction approximately 90 degrees from the 

 heading is called a beam wind. In common 

 usage these two expressions are usually used 

 synonymously, crosswind being favored by avi- 

 ators, and beam wind by mariners. One blow- 

 ing from ahead is called a headwind. One 

 blowing from astern is called a following wind 

 by marine navigators and a tailwind by air 

 navigators. 



crumble — See disintegration. 



crust — The outer shell of the solid earth the lower 

 limit of which is taken generally to be the 

 Mohorovicic discontinuity. The crust varies 

 in thickness from approximately 6 to 7 kil- 

 ometers under the ocean basins to 35 kilometers 

 under the continents. See lithosphere. {See 

 figure for earth structure.) 



crustacean — One of a class (Crustacea) of 

 arthropods which breathe by means of gills or 

 branchiae and with the body commonly covered 

 by a hard shell or crust. The group includes 

 the barnacles, crabs, shrimps, and lobsters. 



crustacean borer — A member of any of three 

 families (Limnoriidae, Sphaeromidae, and 

 Cheluridae) of crustaceans, which, in the first 

 two, resemble pill or sow bugs and in the last, 

 sand fleas. These crustaceans excavate net- 

 works of shallow burrows in wood, the roofs of 

 which are readily eroded by water action. 

 Progressive burrowing and eroding remove a 

 considerable thickness of wood. The most 

 evident and damaging attack is on pilings 

 within the intertidal zone and near the bottom. 

 Continued attack results in the characteristic 

 hourglass shape of severely damaged pilings. 

 Limnoria usually is the initial and principal at- 

 tacker. Members of the other two families gen- 

 erally inhabit and enlarge Limnoria burrows. 

 The attack by at least one species of Limnoria 

 is not inhibited by creosote. See marine borer. 



cryoclinometer — A device for measuring hori- 

 zontal dimensions of a sea ice field from an 

 aircraft. 



cryology — 1. The study of ice and snow. (5) 



2. The study of sea ice. (5) 



3. In Europe, a synonym for glaciology. (5) 

 Note: The term cryology has become almost 



meaningless unless it is defined in context. 

 (59) 



crystalline — The term applied to rocks contain- 

 ing grains of regular polyhedral form bounded 

 by plain surfaces and having an orderly molecu- 

 lar structure. Usually applied to igneous and 

 metamorphic rocks but not to sedimentary 

 rocks. 



ctenophore — (or comh jelly). One of a phylum 

 (Ctenophora) of spherical, pear-shaped, or 

 cylindrical animals of jellylike consistency 

 ranging from less than 1 inch to about 3 feet in 



length. The outer surface of the body bears 

 8 rows of comblike structures. Many species 

 produce glowing-ball luminescence. 



cul-de-sac — 1. An inlet with a single small 

 opening. 



2. A blind lead. 

 (68) 



cum sole — With the sun; hence anticyclonic or 

 clockwise ; the opposite of contra solem. (6) 



curie — (abbreviated c). 1. That quantity of a 

 radioactive nuclide disintegrating at the rate of 

 3.700 X 10^" atoms per second. Several frac- 

 tions of the curie are in common usage. 



Microcurie — (abbreviated /xc). One-mil- 

 lionth of a curie (3.7x10* disintegrations per 

 second) . 



Micro-microcurie — (abbreviated /x/xc). One- 

 millionth of a microcurie (3.7 XIO^^ disintegra- 

 tions per second or 2.22 disintegrations per 

 minute) . Sometimes called a picocurie. 



Millicurie — (abbreviated mc). One-thou- 

 sandth of a curie (3.7x10" disintegrations per 

 second) . 

 (70) 



2. An earlier definition of the curie was : The 

 quantity (grams) of radon in equilibrium with 

 one gram of radium. (41) 



current — A horizontal movement of water. See 

 ocean current, tidal current, nontidal cur- 

 rent, flow. 



current base — The maximum water depth below 

 which currents are ineffective in moving sedi- 

 ment. (2) 



current chart — A map of a water area depicting 

 current speeds and directions by current roses, 

 vectors, or other means. 



current cross section — A graphic presentation 

 of the current shown as a vertical plane per- 

 pendicular to the axis of flow; the horizontal 

 distance between the surface limits is repre- 

 sented by the abscissa, and the depth is shown 

 by the ordinate which increases from the sur- 

 face (zero) down to any depth. See current 

 profile. 



current curve — A graphic presentation of the 

 speed and duration of the tidal current usually 

 shown for areas of reversing tidal currents. 

 The curve is referred to rectangular coordi- 

 nates; the time is represented by the abscissa 

 ' and the speed by the ordinate. The flood speeds 

 are positive, and the ebb speeds are negative 

 values measured from slack (zero speed) . 



current diagram — A graphic presentation show- 

 ing the speed of the flood and ebb currents and 

 the times of slack and strength over a consider- 

 able stretch of the channel of a tidal waterway, 

 the times being referred to tide or current phases 

 at some reference station. ( 50 ) 



current difference — The difference between the 

 time of slack water or strength of current in 

 any locality and the time of the corresponding 



42 



