Are there long paragraphs of description in "The Adventure of the Speckled Band" by Sir Arthur Conan Doyle, and what purpose do they serve?

There is a lengthy descriptive paragraph when Helen Stoner describes for Holmes and Watson the events on the night of her twin sister's death. The paragraph recounts the circumstances surrounding the attack which kills her, thereby providing exposition for the reader and moving the narrative along, as well as delivering the first notable clues for Holmes and Watson. The metallic sound, the low whistle, and the sight of the "speckled band" are vague hints that Holmes immediately begins working on in his formidable mind.
The paragraph that describes Dr. Grimesby Roylott is also lengthy and offers a complete portrait of his physical look from his birdlike face to his gaiters, frock coat, and black top hat. His face is described as "marked with every evil passion" to assist in his characterization.
A third lengthy paragraph of description makes clear to the reader what the setting of the bedroom in Helen Stoner's home looks like. As Holmes sits, taking in every detail of her apartment, the reader receives a strong visual. This will become important in understanding how the murder of Miss Stoner's twin took place in the house and left no trace.