bark vs outer layer

bark

noun
  • The crust formed on barbecued meat that has had a rub applied to it. 

  • The exterior covering of the trunk and branches of a tree. 

  • Peruvian bark or Jesuit's bark, the bark of the cinchona from which quinine is produced. 

  • A vessel, typically with three (or more) masts, with the foremasts (or fore- and mainmasts) square-rigged, and mizzenmast schooner-rigged. 

  • The short, loud, explosive sound uttered by a dog, a fox, and some other animals. 

  • An abrupt loud vocal utterance. 

  • The envelopment or outer covering of anything. 

  • A sailing vessel or boat of any kind. 

  • Hard candy made in flat sheets, for instance out of chocolate, peanut butter, toffee or peppermint. 

verb
  • To make a clamor; to make importunate outcries. 

  • To speak sharply. 

  • To make a short, loud, explosive noise with the vocal organs (said of animals, especially dogs). 

  • To abrade or rub off any outer covering from. 

  • To strip the bark from; to peel. 

  • To cover or inclose with bark, or as with bark. 

  • To girdle. 

outer layer

How often have the words bark and outer layer occurred in a corpus of books? (source: Google Ngram Viewer )