What does the word intrusive mean?

Usage examples for intrusive

  1. There were no fir- branches to part them with intrusive spikes. – The Lilac Sunbonnet by S.R. Crockett
  2. Studying the section of Figure 244, what inference do you draw as to the source of these intrusive sheets? – The Elements of Geology by William Harmon Norton
  3. After this initial exploit Jacobus showed himself anything but intrusive. – 'Twixt Land & Sea by Joseph Conrad